Dell Technologies has released the new PowerEdge R750xa server, a GPU workload-based platform that is designed to support artificial intelligence, machine learning, and high-performance computing solutions. The dual socket/2U platform supports 3^rd Gen Intel Xeon processors (code named Ice Lake). It supports up to 40 cores per processor, has eight memory channels per CPU, and up to 32 DDR4 DIMMs at 3200 MT/s DIMM speed. This server can accommodate up to four double-width PCIe GPUs that are located in the front left and the front right of the server.

Compared with the previous generation PowerEdge C4140 and PowerEdge R740 GPU platform options, the new PowerEdge R750xa server supports larger storage capacity, provides more flexible GPU offerings, and improves the thermal requirement

Figure 1 PowerEdge R750xa server

The NVIDIA A100 GPUs are built on the NVIDIA Ampere architecture to enable double precision workloads. This blog evaluates the new PowerEdge R750xa server and compares its performance with the previous generation PowerEdge C4140 server.

The following table shows the specifications for the NVIDIA GPU that is discussed in this blog and compares the performance improvement from the previous generation.

Table 1 NVIDIA GPU specifications

*with sparsity

Test bed and applications

This blog quantifies the performance improvement of the GPUs with the new PowerEdge GPU platform.

Using a single node PowerEdge R750xa server in the Dell HPC & AI Innovation Lab, we derived all results presented in this blog from this test bed. This section describes the test bed and the applications that were evaluated as part of the study. The following table provides test environment details:

Table 2 Server configuration

The following table provides information about the applications and benchmarks used:

Table 3 Benchmark and application details

LAMMPS

Large-Scale Atomic/Molecular Massively Parallel simulator (LAMMPS) is distributed by Sandia National Labs and the US Department of Energy. LAMMPS is open-source code that has different accelerated models for performance on CPUs and GPUs. For our test, we compiled the binary using the KOKKOS package, which runs efficiently on GPUs.

Figure 2 LAMMPS Performance on PowerEdge R750xa and PowerEdge C4140 servers

With the newer generation GPUs, this application improves 2.4 times compared to single GPU performance. The overall performance from a single server improved twice with the PowerEdge R750xa server and NVIDIA A100 GPUs.

GROMACS

GROMACS is a free and open-source parallel molecular dynamics package designed for simulations of biochemical molecules such as proteins, lipids, and nucleic acids. It is used by a wide variety of researchers, particularly for biomolecular and chemistry simulations. GROMACS supports all the usual algorithms expected from modern molecular dynamics implementation. It is open-source software with the latest versions available under the GNU Lesser General Public License (LGPL).

Figure 3 GROMACS performance on PowerEdge C4140 and r750xa servers

With the newer generation GPUs, this application improved approximately 1.5 times across the dataset compared to single GPU performance. The overall performance from a single server improved 1.5 times with a PowerEdge R750xa server and NVIDIA A100 GPUs.

High-Performance Linpack

High-Performance Linpack (HPL) needs no introduction in the HPC arena. It is a widely used standard benchmark tests in the industry.  

 Figure 4 HPL Performance on the PowerEdge R750xa server with A100 GPU and PowerEdge C4140 server with V100 GPU

Figure 5 Power use of the HPL running on NVIDIA GPUs

From Figure 4 and Figure 5, the following results were observed: 

• Performance—For GPU count, the NVIDIA A100 GPU demonstrates twice the performance of the NVIDIA V100 GPU. Higher memory size, double precision FLOPS, and a newer architecture contribute to the improvement for the NVIDIA A100 GPU.
• Scalability—The PowerEdge R750xa server with four NVIDIA A100-PCIe-40 GB GPUs delivers 3.6 times higher HPL performance compared to one NVIDIA A100-PCIE-40 GB GPU. The NVIDIA A100 GPUs scale well inside the PowerEdge R750xa server for the HPL benchmark.  
• Higher Rpeak—The HPL code on NVIDIA A100 GPUs uses the new double-precision Tensor cores. The theoretical peak for each GPU is 19.5 TFlops, as opposed to 9.7 TFlops. 
• Power—Figure 5 shows power consumption of a complete HPL run with the PowerEdge R750xa server using four A100-PCIe GPUs. This result was measured with iDRAC commands, and the peak power consumption was observed as 2022 Watts. Based on our previous observations, we know that the PowerEdge C4140 server consumes approximately 1800 W of power.

HPCG

Figure 6 Scaling GPU performance data for HPCG Benchmark

As discussed in other blogs, high performance conjugate gradient (HPCG) is another standard benchmark to test data access patterns of sparse matrix calculations. From the graph, we see that the HPCG benchmark scales well with this benchmark resulting in 1.6 times performance improvement over the previous generation PowerEdge C4140 server with an NVIDIA V100 GPU.

The 72 percent improvement in memory bandwidth of the NVIDIA A100 GPU over the NVIDIA V100 GPU contributes to the performance improvement.

Conclusion

In this blog, we introduced the latest generation PowerEdge R750xa platform and discussed the performance improvement over the previous generation PowerEdge C4140 server. The PowerEdge R750xa server is a good option for customers looking for an Intel Xeon scalable CPU-based platform powered with NVIDIA GPUs.

With the newer generation PowerEdge R750xa server and NVIDIA A100 GPUs, the applications discussed in this blog show significant performance improvement.

Next steps

In future blogs, we plan to evaluate NVLINK bridge support, which is another important feature of the PowerEdge R750xa server and NVIDIA A100 GPUs.

Anyone that works with machine learning models trained by optimization methods like stochastic gradient descent (SGD) knows about the power of specialized hardware accelerators for performing a large number of matrix operations that are needed.  Wouldn’t it be great if we all had our own accelerator dense supercomputers?  Unfortunately, the people that manage budgets aren’t approving that plan, so we need to find a workable mix of technology and, yes, the dreaded concept, process to improve our ability to work with hardware accelerators in shared environments.

We have gotten a lot of questions from a customer trying to increase the utilization rates of machines with specialized accelerators.  Good news, there are a lot of big technology companies working on solutions. The rest of the article is going to focus on technology from Dell EMC, NVIDIA, and VMware that is both available today and some that are coming soon.  We also sprinkle in some comments about the process that you can consider.  Please add your thoughts and questions in the comments section below.

We started this latest round of GPU-as-a-service research with a small amount of kit in the Dell EMC Customer Solutions Center in Austin.  We have one Dell EMC PowerEdge R740 with 4 NVIDIA T4 GPUs connected to the system on the PCIe bus.  Our research question is “how can a group of data scientists working on different models with different development tools share these four GPUs?”  We are going to compare two different technology options:

1. VMware Direct Path I/O
2. NVIDIA GPU GRID 9.0

Our server has ESXi installed and is configured as a 1 node cluster in vCenter.  I’m going to skip the configuration of the host BIOS and ESXi and jump straight to creating VMs.  We started off with the Direct Path I/O option.  You should review the article “Using GPUs with Virtual Machines on vSphere – Part 2: VMDirectPath I/O” from VMware before trying this at home.  It has a lot of details that we won’t repeat here. 

There are many approaches available for virtual machine image management that can be set up by the VMware administrators but for this project, we are assuming that our data scientists are building and maintaining the images they use.  Our scenario is to show how a group of Python users can have one image and the R users can have another image that both use GPUs when needed.  Both groups are using primarily TensorFlow and Keras.

Before installing an OS we changed the firmware setting to EFI in the VM Boot Options menu per the article above.  We also used the VM options to assign one physical GPU to the VM using Direct Path I/O before proceeding with any software installs.  It is important for there to be a device present during configuration even though the VM may get used later with or without an assigned GPU to facilitate sharing among users and/or teams.

Once the OS was installed and configured with user accounts and updates, we installed the NVIDIA GPU related software and made two clones of that image since both the R and Python environment setups need the same supporting libraries and drivers to use the GPUs when added to the VM through Direct Path I/O.  Having the base image with an OS plus NVIDIA libraries saves a lot of time if you want a new type of developer environment.

With this much of the setup done, we can start testing assigning and removing GPU devices among our two VMs.  We use VM options to add and remove the devices but only while the VM is powered off. For example, we can assign 2 GPUs to each VM, 4 GPUs to one VM and none to the other or any other combination that doesn’t exceed our 4 available devices.  Devices currently assigned to other VMs are not available in the UI for assignment, so it is not physically possible to create conflicts between VMs. We can NVIDIA’s System Management Interface (nvidia-smi) to list the devices available on each VM.

Remember above when we talked about process, here is where we need to revisit that.  The only way a setup like this works is if people release GPUs from VMs when they don’t need them.  Going a level deeper there will probably be a time when one user or group could take advantage of a GPU but would choose to not take one so other potentially more critical work can have it.  This type of resource sharing is not new to research and development.  All useful resources are scarce, and a lot of efficiencies can be gained with the right technology, process, and attitude

.Before we talk about installing the developer frameworks and libraries, let’s review the outcome we desire. We have 2 or more groups of developers that could benefit from the use of GPUs at different times in their workflow but not always.  They would like to minimize the number of VM images they need and have and would also like fewer versions of code to maintain even when switching between tasks that may or may not have access to GPUs when running.  We talked above about switching GPUs between machines but what happens on the software side?  Next, we’ll talk about some TensorFlow properties that make this easier.

TensorFlow comes in two main flavors for installation tensorflow and tensorflow-gpu.  The first one should probably be called “tensorflow-cpu” for clarity.  For this work, we are only installing the GPU enabled version since we are going to want our VMs to be able to use GPU for any operations that TF supports for GPU devices. The reason that I don’t also need the CPU version when my VM has not been assigned any GPUs is that many operations available in the GPU enabled version of TF have both a CPU and a GPU implantation. When an operation is run without a specific device assignment, any available GPU device will be given priority in the placement.   When the VM does not have a GPU device available the operation will use the CPU implementation.

There are many examples online for testing if you have a properly configured system with a functioning GPU device. This simple matrix multiplication sample is a good starting point.  Once that is working you can move on a full-blown model training with a sample data set like the MNIST character recognition model.  Try setting up a sandbox environment using this article and the VMware blog series above. Then get some experience with allocating and deallocating GPUs to VMs and prove that things are working with a small app.  If you have any questions or comments post them in the feedback section below.

Thanks for reading.

Phil Hummel - Twitter @GotDisk@GotDisk