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vCenter performance improvements from vSphere 6.5 to 6.7: What does 2x mean?

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In a recent blog, the VMware vSphere team shared the following performance improvements in vSphere 6.7 vs. 6.5:

Moreover, with vSphere 6.7 vCSA delivers phenomenal performance improvements (all metrics compared at cluster scale limits, versus vSphere 6.5):
2X faster performance in vCenter operations per second
3X reduction in memory usage
3X faster DRS-related operations (e.g. power-on virtual machine)

As senior engineers within the VMware Performance and vSphere teams, we are writing this blog to provide more details regarding these numbers and to explain how we measured them. We also briefly explain some of the technical details behind these improvements.

Cluster Scale

Let us first explain what all metrics compared at cluster scale limits means. What is cluster scale? Here, it is an environment that includes a vCenter server that is configured for the largest vSphere cluster that VMware currently supports, namely 64 hosts and 8,000 powered-on VMs. This setup represents a high-consolidation environment with 125 VMs per host. Note that this is different from the setup used in our previous blog about vCenter 6.5 performance improvements. The setup in that blog was our datacenter scale environment, which used the largest number of supported hosts (2000) and VMs (25,000), so the numbers from that blog should not be compared to these numbers.

2x and 3x

Let us now explain some of the performance numbers quoted. We produced the numbers by measuring workload runs in our cluster scale setup.

2x vCenter Operations Per Second, vSphere 6.7 vs. 6.5, cluster scale limits. We measure operations per second using an internal benchmark called vcbench. We describe vcbench below under “Benchmark Details.” One of the outputs of this workload is management operations (for example, clone, powerOn, vMotion) performed per second.

  • In 6.5, vCenter was capable of performing approximately 8.3 vcbench operations per second (described below under “Benchmark Details”) in the cluster-scale testbed.
  • In 6.7, vCenter is now capable of performing approximately 16.7 vcbench operations per second.

3x reduction in memory usage. In addition to our vcbench workload, we also include a simplified workload that simply executes a standard workflow: create a VM, power it on, power it off, and delete it. The rapid powerOn and powerOff of VMs in this setup puts more load on the DRS subsystem than the typical vcbench test.

  • In 6.5, the core vCenter process (vpxd) used on average about 10 GB to complete the workflow benchmark (described below under “Benchmark Details”).
  • In 6.7, the core vCenter process used approximately 3 GB to complete this run, while also achieving higher churn (that is, more workflow ‘create/powerOn/powerOff/delete’ cycles completed within the same time period).

3x faster DRS-related operations. In our vcbench workload, we measure not just the overall operations per second, but also the average latencies of individual operations like powerOn (which exercises the majority of the DRS software stack). We issue many concurrent operations, and we measure latency under such load.

  • In 6.5, the average latency of an individual powerOn during a vcbench run was 9.5 seconds.
  • In 6.7, the average latency of an individual powerOn during a vcbench run was 2.8 seconds.

The latencies above reflect the fact that a cluster has 8,000 VMs and many operations in flight at once. As a result, individual operations are slower than if they were simply run on a single-host, single-VM environment.

What does this mean to you as a customer?

As a result of these improvements, customers in high-consolidation environments will see reduced resource consumption due to DRS and reduced latency to generate VMotions for load balancing. Customers will also see faster initial placement of VMs.

Brief Deep Dive into Improvements

Before we describe the improvements, let us first briefly explain how DRS works, at a very high level.

When powering on a VM, vCenter must determine where to place the VM. This is called initial placement. Many subsystems, including DRS and policy management, must be consulted to determine valid hosts on which this VM can run. This phase is called constraint check. Once DRS determines the host on which a VM should be powered on, it registers the VM onto that host and issues the powerOn. This initial placement requires a snapshot of the inventory: by snapshot, we mean that DRS records the current configuration of hosts and VMs in the cluster.

In addition to balancing during initial placement, every 5 minutes, DRS re-examines the load of the cluster and performs a series of computations to generate VMotions that help balance the load across hosts. This phase is called periodic rebalancing. Periodic rebalancing requires an examination of the historical utilization statistics for each host and VM (for example, over the previous hour) in order to determine proper placement.

Finally, as VMs get moved around, the used capacity in resource pools changes. The vCenter server periodically exchanges messages called SpecSyncs with each host to push down the most recent resource pool configuration. The SpecSync operation requires traversing a host’s resource pool structure and changing it to make sure it matches vCenter’s configuration.

With this understanding in mind, let us now give some technical details behind the improvements above. As with our previous blog about vCenter performance improvement, we describe changes in terms of rocks (that is, somewhat large changes to entire subsystems) and pebbles (smaller individual changes throughout the code base).

Rocks

The three main rocks that we address in 6.7 are simplified initial placement, faster resource divvying, and faster SpecSyncs.

Simplified initial placement. As mentioned above, initial placement relies on a snapshot of the current state of the inventory. Creating this snapshot can be a heavyweight operation, requiring a number of data copies and locking of host and cluster data structures to ensure a consistent view of the data. In 6.7, we moved to a lightweight online approach that keeps the state up-to-date in a continuous manner, avoiding snapshots altogether. With this approach, we significantly reduce locking demands and significantly reduce the number of times we need to copy data. In some highly-contended clusters, this reduced the initial placement time from seconds down to milliseconds.

Faster (and more frequent) resource divvying. Divvying is the act of determining the resource allocations for each VM. Every five minutes, the state of the cluster is examined and both divvying and then rebalancing (using VMotion) are performed. To make the divvying phase faster, we performed a number of optimizations.

  • We changed the approach to examining historical usage statistics. Instead of storing metrics for every VM and every host over an hour, we aggregated the data, which allowed us to store a smaller number of metrics per host. This dramatically reduced memory usage and simplified the computation of the desired load for each host.
  • We restructured the code to remove compatibility checks (for example, those that help to determine which VMs can run on which hosts) during this divvying phase. In 6.5 and earlier, divvying a load also involved various host/VM compatibility calculations. Now, we store the compatible matrix and update it when compatibility changes, which is typically infrequent.
  • We have also done significant code refactoring (described below under “Pebbles”) to this code path.

By implementing these changes and making divvying faster in 6.7, we are now able to perform divvying more frequently: once per minute instead of once every five minutes. As a result, resources flow more quickly between resource pools, and we are better able to enforce fairness guarantees in DRS clusters.

Note that periodic load balancing (through VMotion) still occurs every five minutes.

Faster SpecSyncs. To perform a SpecSync, vCenter sends a resource pool configuration to a host. The host must examine this configuration and create a list of changes required to bring that host in sync with vCenter. In 6.5 and earlier, depending on the number of VMs, creating this list of changes could result in hundreds of operations on a host, and the runtime was highly variable. In 6.7, we made this computation more deterministic, reducing the number of operations and lowering the latency appropriately.

Pebbles

In addition to the changes above, we also performed a number of optimizations throughout our code base.

Code Refactoring. In 6.5 and before, admission control decisions were made by multiple independent subsystems within vCenter (for example, DRS would be responsible for some decisions, and HA would make others). In 6.7, we simplified our code such that all admission control decisions are handled by a module within DRS. Reducing multiple copies of this code simplifies debugging and reduces resource usage.

Finer-grained locks. In 6.7, we continued to make strides in reducing the scope of our locks. We introduced finer-grained locks so that DRS would not have to lock an entire VM to examine certain pieces of state. We made similar improvements to both hosts and clusters.

Removal of unnecessary classes, maps, and sets. In refactoring our code, we were able to remove a number of classes and thereby reduce the number of copies of data in our system. The maps and sets that were needed to support these classes could also be removed.

Preferring integers over strings. In many situations, we replaced strings and string comparisons with integers and integer comparisons. This dramatically reduces memory allocation overhead and speeds up comparisons, reducing CPU.

Benchmark Details

We measure Operations Per Second (OPS) using a VMware benchmark called vcbench. (For more details about vcbench, see “Benchmarking Details” in vCenter 6.5 Performance: what does 6x mean?) Briefly, vcbench is a java-based application that takes as an input a runlist, which is a list of management operations to perform. These operations include powering on VMs, cloning VMs, reconfiguring VMs, and migrating VMs, among many other operations. We chose the operations based on an analysis of typical customer management scenarios. The vcbench application uses vSphere APIs to issue these operations to vCenter. The benchmark creates multiple threads and issues operations on those threads in parallel (up to 32). We measure the operations per second by taking the total number of operations performed in a given timeframe (say, 1 hour), and dividing it by the time interval.

Our workflow benchmark is very similar to vcbench. The main difference is that more operations are issued per host at a time. In vcbench, one operation is issued per host at a time, while in workflow, up to 8 operations are issued per host at a time.

In many cases, the size of the VM has an impact on operational latency. For example, a VM with a lot of memory (say, 32 GB) and large disks (say, 100 GB) will take longer to clone because more memory will need to be snapshotted, and more disk data will need to be copied. To minimize the impact of the disk subsystem in our measurements, we use small VMs (<4GB memory, < 8GB disk).

Because we limit ourselves to 32 threads per vCenter in this single-cluster setup, throughput numbers are smaller than for our datacenter-at-scale setups (2,000 hosts; 25,000 VMs), which use up to 256 concurrent threads per vCenter.

Summary

In this blog, we have described some of the performance improvements in vCenter from 6.5 to 6.7. A variety of improvements to DRS have led to improved throughput and reduced resource usage for our vcbench workload in a cluster scale setup of 64 hosts and 8,000 powered-on VMs. Many of these changes also apply to larger datacenter-scale setups, although the scope of improvement may not be as pronounced.

Acknowledgments

The vCenter improvements described in this blog are the results of thousands of person-hours from vCenter developers, performance engineers, and others throughout VMware. We are deeply grateful to them for making this happen.

Authors

Zhelong Pan is a senior staff engineer in the Distributed Resource Management Team at VMware. He works on cluster management, including shared resource allocation, VM placement, and load balancing. He is interested in performance optimizations, including virtualization performance and management software performance. He has been at VMware since 2006.

Ravi Soundararajan is a principal engineer in the Performance Group at VMware. He works on vCenter performance and scalability, from the UI to the server to the database to the hypervisor management agents. He has been at VMware since 2003, and he has presented on the topic of vCenter Performance at VMworld from 2013-2017. His Twitter handle is @vCenterPerfGuy.

Addressing Meltdown/Spectre in VMmark

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The recently described Meltdown/Spectre vulnerabilities have implications throughout the tech industry, and the VMmark virtualization benchmark is no exception. In deciding how to approach the issue, the VMmark team’s goal was to address the impact of the these vulnerabilities while maintaining the value and integrity of the benchmark.

Applying the full set of currently available Meltdown/Spectre mitigations is likely to have a significant impact on VMmark scores. Because the mitigations are expected to continue evolving for some time, that impact might even change. If the VMmark team were to require the full set of mitigations in order for a submission to be compliant, that might make new submissions non-competitive with older ones, and also introduce more “noise” into VMmark scores as the mitigations evolve. While our intention for the future is that eventually all new VMmark results will be obtained on virtualization platforms that have the full set of Meltdown/Spectre mitigations, we have chosen to take a gradual approach.

Beginning May 8, 2018, all newly-published VMmark results must comply with a number of new requirements related to the Meltdown and Spectre vulnerabilities. These requirements are detailed in Appendix C of the latest edition of the VMmark User’s Guide.

Before performing any VMmark benchmark runs intended for publication, check the VMmark download page to make sure you’re using the latest edition of the VMmark User’s Guide.  If you have questions, you can reach the VMmark team at vmmark-info@vmware.com.

SQL Server Performance of VMware Cloud on AWS

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In the past, I’ve always benchmarked performance of SQL Server VMs on vSphere with “on-premises” infrastructure.  Given the skyrocketing interest in the cloud, I was very excited to get my hands on VMware Cloud on AWS – just in time for Amazon’s AWS Summit!

A key question our customers have is: how well do applications (like SQL Server) perform in our cloud?  Well, I’m happy to report that the answer is great!

VMware Cloud on AWS Environment

First, here is a screenshot of what my vSphere-powered Software-Defined Data Center (SDDC) looks like:vSphere Client - VMware Cloud on AWSThis screenshot shows several notable items:

  • The HTML5-based vSphere Client interface should be very familiar to vSphere administrators, making the move to the cloud extremely easy
  • This SDDC instance was auto-provisioned with 4 ESXi hosts and 2TB of memory, all of which were pre-configured with vSAN storage and NSX networking.
    • Each host is configured with two CPUs (Intel Xeon Processor E5-2686 v4); each socket contains 18 cores running at 2.3GHz, resulting in 144 physical cores in the cluster. For more information, see the VMware Cloud on AWS Technical Overview
  • Virtual machines are provisioned within the customer workload resource pool, and vSphere DRS automatically handles balancing the VMs across the compute cluster.

Benchmark Methodology

To measure SQL Server database performance, I used HammerDB, an open-source database load testing and benchmarking tool.  It implements a TPC-C like workload, and reports throughput in TPM (Transactions Per Minute).

To measure how well performance scaled in this cloud, I started with a single 8 vCPU, 32GB RAM VM for the SQL Server database.  To drive the workload, I created a 4 vCPU, 4GB RAM HammerDB driver VM.  I then cloned these VMs to measure 2 database VMs being driven simultaneously:HammerDB and SQL Server VMs in VMware Cloud on AWS

I then doubled the number of VMs again to 4, 8, and finally 16.  As with any benchmark, these VMs were completely driven up to saturation (100% load) – “pedal to the metal”!

Results

So, how did the results look?  Well, here is a graph of each VM count and the resulting database performance:

As you can see, database performance scaled great; when running 16 8-vCPU VMs, VMware Cloud on AWS was able to sustain 6.7 million database TPM!

I’ll be detailing these benchmarks more in an upcoming whitepaper, but wanted to share these results right away.  If you have any questions or feedback, please leave me a comment!

ESX IP Storage Troubleshooting Best Practice White Paper

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We have published an ESX IP Storage Troubleshooting Best Practice white paper in which we recommend vSphere customers deploying ESX IP storage over 10G networks to include 10G packet capture systems as a best practice to ensure network visibility.

The white paper explores the challenges and alternatives for packet capture in a vSphere environment with IP storage (NFS, iSCSI) datastores over a 10G network, and explains why traditional techniques for capturing packet traces on 1G networks will suffer from severe limitations (capture drops and inaccurate timestamps) when used for 10G networks. Although commercial 10G packet capture systems are commonly available, they may be beyond the budget of some vSphere customers. We present the design of a self-assembled 10G packet capture solution that can be built using commercial components relatively inexpensively. The self-assembled solution is optimized for common troubleshooting scenarios where short duration packet captures can satisfy most analysis requirements.

Our experience troubleshooting a large number of IP storage issues has shown that the ability to capture and analyze packet traces in an ESX IP storage environment can significantly reduce the mean time to resolution for serious functional and performance issues. When reporting an IP storage problem to VMware or to a storage array vendor, an accompanying packet trace file is a great piece of evidence that can significantly reduce the time required by the responsible engineering teams to identify the problem.

Performance Comparison of Containerized Machine Learning Applications Running Natively with Nvidia vGPUs vs. in a VM – Episode 4

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This article is by Hari Sivaraman, Uday Kurkure, and Lan Vu from the Performance Engineering team at VMware.

Performance Comparison of Containerized Machine Learning Applications

Docker containers [6] are rapidly becoming a popular environment in which to run different applications, including those in machine learning [1, 2, 3]. NVIDIA supports Docker containers with their own Docker engine utility, nvidia-docker [7], which is specialized to run applications that use NVIDIA GPUs.

The nvidia-docker container for machine learning includes the application and the machine learning framework (for example, TensorFlow [5]) but, importantly, it does not include the GPU driver or the CUDA toolkit.

Docker containers are hardware agnostic so, when an application uses specialized hardware like an NVIDIA GPU that needs kernel modules and user-level libraries, the container cannot include the required drivers. They live outside the container.

One workaround here is to install the driver inside the container and map its devices upon launch. This workaround is not portable since the versions inside the container need to match those in the native operating system.

The nvidia-docker engine utility provides an alternate mechanism that mounts the user-mode components at launch, but this requires you to install the driver and CUDA in the native operating system before launch. Both approaches have drawbacks, but the latter is clearly preferable.

In this episode of our series of blogs [8, 9, 10] on machine learning in vSphere using GPUs, we present a comparison of the performance of MNIST [4] running in a container on CentOS executing natively with MNIST running in a container inside a CentOS VM on vSphere. Based on our experiments, we demonstrate that running containers in a virtualized environment, like a CentOS VM on vSphere, suffers no performance penlty, while benefiting from the tremenduous management capabilities offered by the VMware vSphere platform.

Experiment Configuration and Methodology

We used MNIST [4] to compare the performance of containers running natively with containers running inside a VM. The configuration of the VM and the vSphere server we used for the “virtualized container” is shown in Table 1. The configuration of the physical machine used to run the container natively is shown in Table 2.

vSphere  6.0.0, build 3500742
Nvidia vGPU driver 367.53
Guest OS CentOS Linux release 7.4.1708 (Core)
CUDA driver 8.0
CUDA runtime 7.5
Docker 17.09-ce-rc2

⇑ Table 1. Configuration of VM used to run the nvidia-docker container

Nvidia driver 384.98
Operating system CentOS Linux release 7.4.1708 (Core)
CUDA driver 8.0
CUDA runtime 7.5
Docker 17.09-ce-rc2

⇑ Table 2. Configuration of physical machine used to run the nvidia-docker container

The server configuration we used is shown in Table 3 below. In our experiments, we used the NVIDIA M60 GPU in vGPU mode only. We did not use the Direct I/O mode. In the scenario in which we ran the container inside the VM, we first installed the NVIDIA vGPU drivers in vSphere and inside the VM, then we installed CUDA (driver 8.0 with runtime version 7.5), followed by Docker and nvidia-docker [7]. In the case where we ran the container natively, we installed the NVIDIA driver in CentOS running natively, followed by CUDA (driver 8.0 with runtime version 7.5),  Docker and finally, nvidia-docker [7]. In both scenarios we ran MNIST and we measured the run time for training using a wall clock.

⇑ Figure 1. Testbed configuration for comparison of the performance of containers running natively vs. running in a VM

Model Dell PowerEdge R730
Processor type Intel® Xeon® CPU E5-2680 v3 @ 2.50GHz
CPU cores 24 CPUs, each @ 2.5GHz
Processor sockets 2
Cores per socket 14
Logical processors 48
Hyperthreading Active
Memory 768GB
Storage Local SSD (1.5TB), Storage Arrays, Local Hard Disks
GPUs 2x M60 Tesla

⇑ Table 3. Server configuration

Results

The measured wall-clock run times for MNIST are shown in Table 4 for the two scenarios we tested:

  1. Running in an nvidia-docker container in CentOS running natively.
  2. Running in an nvidia-docker container inside a CentOS VM on vSphere.

From the data, we can clearly see that there is no measurable performance penalty for running a container inside a VM as compred to running it natively.

Configuration Run time for MNIST as measured by a wall clock
Nvidia-docker container in CentOS running natively 44 minutes 53 seconds
Nvidia-docker container running in a CentOS VM on vSphere 44  minutes 57 seconds

⇑ Table 4. Comparison of the run-time for MNIST running in a container on native CentOS vs. in a container in virtualized CentOS

Takeaways

  • Based on the results shown in Table 4, it is clear that there is no measurable performance impact due to running a containerized application in a virtual environment as opposed to running it natively. So, from a performance perspective, there is no penalty for using a virtualized environment.
  • It is important to note that since containers do not include the GPU driver or the CUDA environment, both of these components need to be installed separately. It is in this aspect that a virtualized environment offers a superior user experience; an nvidia-docker container in CentOS running natively requires that any existing GPU and CUDA drivers be removed if the version of the drivers does not match that required by the container. Uninstalling and re-installing the correct drivers is often a challenging and time consuming task. However, in a virtualized environment, you can, in advance, create and store in a repository, a number of CentOS VMs with different VGPU and CUDA drivers. When you need to run an application in an nvidia-docker container, just clone the VM with the correct drivers, load the container, and run with no performance penalty. In such a scenario, running in a virtualized environment does not require you to uninstall and re-install the correct drivers, which saves both time and considerable frustration. This issue of uninstalling and re-installing drivers in a native environment becomes considerably more difficult if there are multiple container users on the system; in such a scenario, all the containers need to be migrated to use the new drivers, or the user who needs a new driver will have to wait until all the other users are done before a system administrator can upgrade the GPU drivers on the native CentOS.

Future Work

In this blog, we presented the performance results of running MNIST in a single container. We plan to run MNIST in multiple containers running concurrently in both a virtualized environment and on CentOS executing natively, and report the measured run times. This will provide a comparison of the performance as we scale up the number of containers.

References

  1. Google Cloud Platform: Cloud AI. https://cloud.google.com/products/machine-learning/
  2. Wikipedia: Deep Learning. https://en.wikipedia.org/wiki/Deep_learning
  3. NVIDIA GPUs – The Engine of Deep Learning. https://developer.nvidia.com/deep-learning
  4. The MNIST Database of Handwritten Digits. http://yann.lecun.com/exdb/mnist/
  5. TensorFlow: An Open-Source Software Library for Machine Intelligence. https://www.tensorflow.org
  6. Wikipedia: Operating-System-Level Virtualization. https://en.wikipedia.org/wiki/Operating-system-level_virtualization
  7. NVIDIA Docker: GPU Server Application Deployment Made Easy. https://devblogs.nvidia.com/parallelforall/nvidia-docker-gpu-server-application-deployment-made-easy/
  8. Episode 1: Performance Results of Machine Learning with DirectPath I/O and GRID vGPU. https://blogs.vmware.com/performance/2016/10/machine-learning-vsphere-nvidia-gpus.html
  9. Episode 2: Machine Learning on vSphere 6 with NVIDIA GPUs. https://blogs.vmware.com/performance/2017/03/machine-learning-vsphere-6-5-nvidia-gpus-episode-2.html
  10. Episode 3: Performance Comparison of Native GPU to Virtualized GPU and Scalability of Virtualized GPUs for Machine Learning. https://blogs.vmware.com/performance/2017/10/episode-3-performance-comparison-native-gpu-virtualized-gpu-scalability-virtualized-gpus-machine-learning.html 

Performance of SQL Server 2017 for Linux VMs on vSphere 6.5

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Microsoft SQL Server has long been one of the most popular applications for running on vSphere virtual machines.  Last year there was quite a bit of excitement when Microsoft announced they were bringing SQL Server to Linux.  Over the last year Microsoft has had quite a bit of interest in SQL Server for Linux and it was announced at Microsoft Ignite last month that it is now officially launched and generally available.

VMware and Microsoft have collaborated to validate and support the functionality and performance scalability of SQL Server 2017 on vSphere-based Linux VMs.  The results of that work show SQL Server 2017 for Linux installs easily and has great performance within VMware vSphere virtual machines. VMware vSphere is a great environment to be able to try out the new Linux version of SQL Server and be able to also get great performance.

Using CDB, a cloud database benchmark developed by the Microsoft SQL Server team, we were able to verify that the performance of SQL Server for Linux in a vSphere virtual machine was similar to other non-virtualized and virtualized operating systems or platforms.

Our initial reference test size was relatively small, so we wanted to try out testing larger sizes to see how well SQL Server 2017 for Linux performed as the VM size was scaled up.  For the test, we used a four socket Intel Xeon E7-8890 v4 (Broadwell)-based server with 96 cores (24 cores per socket).  The initial test began with a 24 virtual CPU VM to match the number of physical cores of a single socket.  Additional tests were run by increasing the size of the VM by 24 vCPUs for each test until, in the final test, the VM had 96 total vCPUs.  We configured the virtual machine with 512 GB of RAM and separate log and data disks on an SSD-based Fibre Channel SAN.  We used the same best practices for SQL Server for Linux as what we normally use for the windows version as documented in our published best practices guide for SQL Server on vSphere.

The results showed that SQL Server 2017 for Linux scaled very well as the additional vCPUs were added to the virtual machine. SQL Server 2017 for Linux is capable of scaling up to handle very large databases on VMware vSphere 6.5 Linux virtual machines.

Skylake Update – Oracle Database Performance on vSphere 6.5 Monster Virtual Machines

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We were able to get one of the new four-socket Intel Skylake based servers and run some more tests. Specifically we used the Xeon Platinum 8180 processors with 28 cores each. The new data has been added to the Oracle Monster Virtual Machine Performance on VMware vSphere 6.5 whitepaper. Please check out the paper for the full details and context of these updates.

The generational testing in the paper now includes a fifth generation with a 112 vCPU virtual machine running on the Skylake based server. Performance gain from the initial 40 vCPU VM on Westmere-EX to the Skylake based 112 vCPU VM is almost 4x.

The performance gained from Hyper-Threading was also updated and shows a 27% performance gain from the use of Hyper-Threads. The test was conducted by running two 112 vCPU VMs at the same time so that all 224 logical threads are active. The total throughput from the two VMs is then compared with the throughput from a single VM.

My colleague David Morse has also updated his SQL Server monster virtual machine whitepaper with Skylake data as well.

Episode 3: Performance Comparison of Native GPU to Virtualized GPU and Scalability of Virtualized GPUs for Machine Learning

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In our third episode of machine learning performance with vSphere 6.x, we look at the virtual GPU vs. the physical GPU. In addition, we extend the performance results of machine learning workloads using VMware DirectPath I/O (passthrough) vs. NVIDIA GRID vGPU that have been partially addressed in previous episodes:

Machine Learning with Virtualized GPUs

Performance is one of the biggest concerns that keeps high performance computing (HPC) users from choosing virtualization as the solution for deploying HPC applications despite virtualization benefits such as reduced administration costs, resource utilization efficiency, energy saving, and security. However, with the constant evolution of virtualization technologies, the performance gaps between bare metal and virtualization have almost disappeared, and, in some use cases, virtualized applications can achieve better performance than running on bare metal because of the intelligent and highly optimized resource utilization of hypervisors. For example, a prior study [1] shows that vector machine applications running on a virtualized cluster of 10 servers have a better execution time than running on bare metal.

Virtual GPU vs. Physical GPU

To understand the performance impact of machine learning with GPUs using virtualization, we used a complex language modeling application—predicting next words given a history of previous words using a recurrent neural network (RNN) with 1500 Long Short Term Memory (LSTM) units per layer, on the Penn Treebank (PTB) dataset [2, 3], which has:

  • 929,000 training words
  • 73,000 validation words
  • 82,000 test words
  • 10,000 vocabulary words

We tested three cases:

  • A physical GPU installed on bare metal (this is the “native” configuration)
  • A DirectPath I/O GPU inside a VM on vSphere 6
  • A GRID vGPU (that is, an M60-8Q vGPU profile with 8GB memory) inside a VM on vSphere 6

The VM in the last two cases has 12 virtual CPUs (vCPUs), 60GB RAM, and 96GB SSD storage.

The benchmark was implemented using TensorFlow [4], which was also used for the implementation of the other machine learning benchmarks in our experiments. We used CUDA 7.5, cuDNN 5.1, and CentOS 7.2 for both native and guest operating systems. These test cases were run on a Dell PowerEdge R730 server with dual 12-core Intel Xeon Processors E5-2680 v3, 2.50 GHz sockets (24 physical core, 48 logical with hyperthreading enabled), 768 GB memory, and an SSD (1.5 TB). This server also had two NVIDIA Tesla M60 cards (each has two GPUs) for a total of 4 GPUs where each had 2048 CUDA cores, 8GB memory, 36 x H.264 video 1080p 30 streams, and could support 1–32 GRID vGPUs whose memory profiles ranged from 512MB to 8GB. This experimental setup was used for all tests presented in this blog (Figure 1, below).

Figure 1. Testbed configurations for native GPU vs. virtual GPU comparison

The results in Figure 2 (below) show the relative execution times of DirectPath I/O and GRID vGPU compared to native GPU. Virtualization introduces a 4% overhead—the performance of DirectPath I/O and GRID vGPU are similar. These results are consistent with prior studies of virtual GPU performance with passthrough where overheads in most cases are less than 5% [5, 6].

Figure 2. DirectPath I/O and NVIDIA GRID vs. native GPU

GPU vs. CPU in a Virtualization Environment

One important benefit of using GPU is the shortening of the long training times of machine learning tasks, which has boosted the results of AI research and developments in recent years. In many cases, it helps to reduce execution times from weeks/days to hours/minutes. We illustrate this benefit in Figure 3 (below), which shows the training time with and without vGPU for two applications:

  • RNN with PTB (described earlier)
  • CNN with MNIST—a handwriting recognizer that uses a convolution neural network (CNN) on the MNIST dataset [7].

From the results, we see that the training time for RNN on PTB with CPU was 7.9 times higher than with vGPU training time (Figure 3-a).  The training time for CNN on MNIST with CPU was 10.1 times higher than with the vGPU training time (Figure 3-b). The VM used in this test has 1 vGPU, 12 vCPUs, 60 GB memory, 96 GB of SSD storage and the test setup is similar to that of the above experiment.

Figure 3. Normalized training time of PTB, MNIST with and without vGPU

As the test results show, we can successfully run machine learning applications in a vSphere 6 virtualized environment, and its performance is similar to training times for machine learning applications running in a native configuration (not virtualized) using physical GPUs.

But what about a passthrough scenario? How does a machine learning application run in a vSphere 6 virtual machine using a passthrough to the physical GPU vs. using a virtualized GPU? We present our findings in the next section.

Comparison of DirectPath I/O and GRID vGPU

We evaluate the performance, scalability, and other benefits of DirectPath I/O and GRID vGPU. We also provide some recommendations of the best use cases for each virtual GPU solutions.

Performance

To compare the performance of DirectPath I/O and GRID vGPU, we benchmarked them with RNN on PTB, and CNN on MNIST and CIFAR-10. CIFAR-10 [8] is an object classification application that categorizes RGB images of 32×32 pixels into 10 categories: airplane, automobile, bird, cat, deer, dog, frog, horse, ship, and truck. MNIST is a handwriting recognition application. Both CIFAR-10 and MNIST use a convolutional neural network. The language model used to predict words is based on history using a recurrent neural network. The dataset used is The Penn Tree Bank (PTB).

Fig. 4. Performance comparison of DirectPath I/O and GRID vGPU.

The results in Figure 4 (above) show the comparative performance of the two virtualization solutions in which DirectPath I/O achieves slightly better performance than GRID vGPU. This improvement is due to the passthrough mechanism of DirectPath I/O adding minimal overhead to GPU-based workloads running inside a VM. In Figure 4-a, DirectPath I/O is about 5% faster than GRID vGPU for MNIST, and they have the same performance with PTB. For CIFAR-10, DirectPath I/O can process about 13% more images per second than GRID vGPU. We use images per second for CIFAR-10 because it is a frequently used metric for this dataset. The VM in this experiment has 12 vCPU, 60GB VRAM and one GPU (either DirectPath I/O or GRID vGPU).

Scalability

We look at two types of scalability: user and GPU.

User Scalability

In a cloud environment, multiple users can share physical servers, which helps to better utilize resources and save cost. Our test server with 4 GPUs can allow up to 4 users needing a GPU. Alternatively, a single user can have four VMs with a vGPU.  The number of virtual machines run per machine in a cloud environment is typically high to increase utilization and lower costs [9]. Machine learning workloads are typically much more resource intensive and using our 4 GPU test systems for up to only 4 users reflects this.

Figure 5. Scaling the number of VMs with vGPU on CIFAR-10

Figure 5 (above) presents the scalability of users on CIFAR-10 from 1 to 4 where each uses a VM with one GPU, and we normalize images per second to that of the DirectPath I/O – 1 VM case (Figure 5-a).  Similar to the previous comparison, DirectPath I/O and GRID vGPU show comparable performance as the number of VMs with GPUs scale. Specifically, the performance difference between them is 6%–10% for images per second and 0%–1.5% for CPU utilization. This difference is not significant when weighed against the benefits that vGPU brings. Because of its flexibility and elasticity, it is a good option for machine learning workloads. The results also show that the two solutions scale linearly with the number of VMs both in terms of execution time and CPU resource utilization. The VMs used in this experiment have 12 vCPUs, 16GB memory, and 1 GPU (either DirectPath I/O or GRID vGPU).

GPU Scalability

For machine learning applications that need to build very large models or in which the datasets cannot fit into a single GPU, users can use multiple GPUs to distribute the workloads among them and speed up the training task further. On vSphere, applications that require multiple GPUs can use DirectPath I/O passthrough to configure VMs with as many GPUs as required. This capability is limited for CUDA applications using GRID vGPU because only 1 vGPU per VM is allowed for CUDA computations.

We demonstrate the efficiency of using multiple GPUs on vSphere by benchmarking the CIFAR-10 workload and using the metric of images per second (images/sec) to compare the performance of CIFAR-10 on a VM with different numbers of GPUs scaling from 1 to 4 GPUs.

From the results in Figure 6 (below), we found that the images processed per second improves almost linearly with the number of GPUs on the host (Figure 6-a). At the same time, their CPU utilization also increases linearly (Figure 6-b). This result shows that machine learning workloads scale well on the vSphere platform. In the case of machine learning applications that require more GPUs than the physical server can support, we can use the distributed computing model with multiple distributed processes using GPUs running on a cluster of physical servers. With this approach, both DirectPath I/O and GRID vGPU can be used to enhance scalability with a very large number of GPUs.

Figure 6. Scaling the number of GPUs per VM on CIFAR-10

How to Choose Between DirectPath I/O and GRID vGPU

For DirectPath I/O

From the above results, we can see that DirectPath I/O and GRID vGPU have similar performance and low overhead compared to the performance of native GPU, which makes both good choices for machine learning applications in virtualized cloud environments. For applications that require short training times and use multiple GPUs to speed up machine learning tasks, DirectPath I/O is a suitable option because this solution supports multiple GPUs per VM. In addition, DirectPath I/O supports a wider range of GPU devices, and so can provide a more flexible choice of GPU for users.

For GRID vGPU

When each user needs a single GPU, GRID vGPU can be a good choice. This configuration provides a higher consolidation of virtual machines and leverages the benefits of virtualization:

  • GRID vGPU allows the flexible use of the device because vGPU supports both shared GPU (multiple users per physical machine) and dedicated GPU (one user per physical GPU). Mixing and switching among machine learning, 3D graphics, and video encoding/decoding workloads using GPUs is much easier and allows for more efficient use of the hardware resource. Using GRID solutions for machine learning and 3D graphics allows cloud-based services to multiplex the GPUs among more concurrent users than the number of physical GPUs in the system. This contrasts with DirectPath I/O, which is the dedicated GPU solution, where the number of concurrent users are limited to the number of physical GPUs.
  • GRID vGPU reduces administration cost because its deployment and maintenance does not require server reboot, so no down time is required for end users. For example, changing the vGPU profile of a virtual machine does not require a server reboot. Any changes to DirectPath I/O configuration requires a server reboot. GRID vGPU’s ease of management reduces the time and the complexity of administering and maintaining the GPUs. This benefit is particularly important in a cloud environment where the number of managed servers would be very large.

Conclusion

Our tests show that virtualized machine learning workloads on vSphere with vGPUs offer near bare-metal performance.

References

  1. Jaffe, D. Big Data Performance on vSphere 6. (August 2016). http://www.vmware.com/content/dam/digitalmarketing/vmware/en/pdf/techpaper/bigdata-perf-vsphere6.pdf.
  2. Zaremba, W., Sutskever,I., Vinyals, O.: Recurrent Neural Network Regularization. In: arXiv:1409.2329 (2014).
  3. Taylor, A., Marcus, M., Santorini, B.: The Penn Treebank: An Overview. In: Abeille, A. (ed.). Treebanks: the state of the art in syntactically annotated corpora. Kluwer (2003).
  4. Tensorflow Homepage, https://www.tensorflow.org
  5. Vu, L., Sivaraman, H., Bidarkar, R.: GPU Virtualization for High Performance General Purpose Computing on the ESX hypervisor. In: Proc. of the 22nd High Performance Computing Symposium (2014).
  6. Walters, J.P., Younge, A.J., Kang, D.I., Yao, K.T., Kang, M., Crago, S.P., Fox, G.C.: GPU Passthrough Performance: A Comparison of KVM, Xen, VMWare ESXi, and LXC for CUDA and OpenCL Applications. In: Proceedings of 2014 IEEE 7th International Conference on Cloud Computing (2014).
  7. LeCun, Y., Bottou, L., Bengio, Y., Haffner, P.: Gradient-based learning applied to document recognition. In: Proceedings of the IEEE, 86(11):2278-2324 (November 1998).
  8. Multiple Layers of Features from Tiny Images, https://www.cs.toronto.edu/~kriz/cifar.html
  9. Pandey, A., Vu, L., Puthiyaveettil, V., Sivaraman, H., Kurkure, U., Bappanadu, A.: An Automation Framework for Benchmarking and Optimizing Performance of Remote Desktops in the Cloud. In: To appear in Proceedings of the 2017 International Conference on High Performance Computing & Simulation (2017).

Updated – SQL Server VM Performance with vSphere 6.5, October 2017

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Back in March, I published a performance study of SQL Server performance with vSphere 6.5 across multiple processor generations.  Since then, Intel has released a brand-new processor architecture: the Xeon Scalable platform, formerly known as Skylake.

Our team was fortunate enough to get early access to a server with these new processors inside – just in time for generating data that we presented to customers at VMworld 2017.

Each Xeon Platinum 8180 processor has 28 physical cores (pCores), and with four processors in the server, there was a whopping 112 pCores on one physical host!  As you can see, that extra horsepower provides nice database server performance scaling:

Generational SQL Server VM Database Performance

Generational SQL Server VM Database Performance

For more details and the test results, take a look at the updated paper:
Performance Characterization of Microsoft SQL Server on VMware vSphere 6.5

Highlights from: The Extreme Performance Series at VMworld 2017

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Thank you to everyone who attended VMworld 2017 and especially those that participated in this year’s Extreme Performance Series.  While the conference is wrapped up, the content created and presented there, is now available to everyone! So grab a chair and advance your performance skill set.

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