==================== Tune GPU Performance ==================== .. contents:: This tutorial will guide you step-by-step through how to conduct profiling and performance tuning using built-in timer, **nvprof** and **nvvp**. - What is profiling? - Why we need profiling? - How to do profiling? - Profile tools - Hands-on Tutorial - Profiling tips What's profiling? ================= In software engineering, profiling is a form of dynamic program analysis that measures the space (memory) or time complexity of a program, the usage of particular instructions, or the frequency and duration of function calls. Most commonly, profiling information serves to aid program optimization. Briefly, profiler is used to measure application performance. Program analysis tools are extremely important for understanding program behavior. Simple profiling can tell you that how long does an operation take? For advanced profiling, it can interpret why does an operation take a long time? Why we need profiling? ====================== Since training deep neural network typically take a very long time to get over, performance is gradually becoming the most important thing in deep learning field. The first step to improve performance is to understand what parts are slow. There is no point in improving performance of a region which doesn’t take much time! How to do profiling? ==================== To achieve maximum performance, there are five steps you can take to reach your goals. - Profile the code - Find the slow parts - Work out why they’re slow - Make them fast - Profile the code again Usually, processor has two key performance limits include float point throughput and memory throughput. For GPU, it also need more parallelism to fulfill its potential. This is why they can be so fast. Profiler Tools ============== For general GPU profiling, a bunch of tools are provided from both NVIDIA and third party. **nvprof** is Nvidia profiler and **nvvp** is (GUI based) Nvidia visual profiler. In this tutorial, we will focus on nvprof and nvvp. :code:`test_GpuProfiler` from :code:`paddle/legacy/math/tests` directory will be used to evaluate above profilers. .. literalinclude:: ../../../../paddle/legacy/math/tests/test_GpuProfiler.cpp :language: c++ :lines: 137-151 :linenos: The above code snippet includes two methods, you can use any of them to profile the regions of interest. 1. :code:`REGISTER_TIMER_INFO` is a built-in timer wrapper which can calculate the time overhead of both cpu functions and cuda kernels. 2. :code:`REGISTER_GPU_PROFILER` is a general purpose wrapper object of :code:`cudaProfilerStart` and :code:`cudaProfilerStop` to avoid program crashes when CPU version of PaddlePaddle invokes them. You can find more details about how to use both of them in the next session. Hands-on Approach ================= Built-in Timer -------------- To enable built-in timer in PaddlePaddle, first you have to add :code:`REGISTER_TIMER_INFO` into the regions of you interest. Then, all information could be stamped in the console via :code:`printStatus` or :code:`printAllStatus` function. As a simple example, consider the following: 1. Add :code:`REGISTER_TIMER_INFO` and :code:`printAllStatus` functions (see the emphasize-lines). .. literalinclude:: ../../../../paddle/legacy/math/tests/test_GpuProfiler.cpp :language: c++ :lines: 137-151 :emphasize-lines: 8-12,14 :linenos: 2. Configure cmake with **WITH_TIMER** and recompile PaddlePaddle. .. code-block:: bash cmake .. -DWITH_TIMER=ON make 3. Execute your code and observe the results (see the emphasize-lines). .. code-block:: bash :emphasize-lines: 1,12-15 > ./paddle/legacy/math/tests/test_GpuProfiler I1117 11:13:42.313065 2522362816 Util.cpp:155] commandline: ./paddle/legacy/math/tests/test_GpuProfiler I1117 11:13:42.845065 2522362816 Util.cpp:130] Calling runInitFunctions I1117 11:13:42.845208 2522362816 Util.cpp:143] Call runInitFunctions done. [==========] Running 1 test from 1 test case. [----------] Global test environment set-up. [----------] 1 test from Profiler [ RUN ] Profiler.BilinearFwdBwd I1117 11:13:42.845310 2522362816 test_GpuProfiler.cpp:114] Enable GPU Profiler Stat: [testBilinearFwdBwd] "numSamples = 10, channels = 16, im gSizeX = 64, imgSizeY = 64" I1117 11:13:42.850154 2522362816 ThreadLocal.cpp:37] thread use undeterministic rand seed:20659751 I1117 11:13:42.981501 2522362816 Stat.cpp:130] ======= StatSet: [GlobalStatInfo] status ====== I1117 11:13:42.981539 2522362816 Stat.cpp:133] Stat=testBilinearFwdBwd total=136.141 avg=136.141 max=136.141 min=136.141 count=1 I1117 11:13:42.981572 2522362816 Stat.cpp:141] ======= BarrierStatSet status ====== I1117 11:13:42.981575 2522362816 Stat.cpp:154] -------------------------------------------------- [ OK ] Profiler.BilinearFwdBwd (136 ms) [----------] 1 test from Profiler (136 ms total) [----------] Global test environment tear-down [==========] 1 test from 1 test case ran. (136 ms total) [ PASSED ] 1 test. nvprof profiler --------------- To use this command line profiler **nvprof**, you can simply issue the following command: 1. Add :code:`REGISTER_GPU_PROFILER` function (see the emphasize-lines). .. literalinclude:: ../../../../paddle/legacy/math/tests/test_GpuProfiler.cpp :language: c++ :lines: 137-151 :emphasize-lines: 6-7 :linenos: 2. Configure cmake with **WITH_PROFILER** and recompile PaddlePaddle. .. code-block:: bash cmake .. -DWITH_PROFILER=ON make 3. Use Nvidia profiler **nvprof** to profile the binary. .. code-block:: bash nvprof ./paddle/legacy/math/tests/test_GpuProfiler Then, you can get the following profiling result: .. code-block:: bash ==78544== Profiling application: ./paddle/legacy/math/tests/test_GpuProfiler ==78544== Profiling result: Time(%) Time Calls Avg Min Max Name 27.60% 9.6305ms 5 1.9261ms 3.4560us 6.4035ms [CUDA memcpy HtoD] 26.07% 9.0957ms 1 9.0957ms 9.0957ms 9.0957ms KeBilinearInterpBw 23.78% 8.2977ms 1 8.2977ms 8.2977ms 8.2977ms KeBilinearInterpFw 22.55% 7.8661ms 2 3.9330ms 1.5798ms 6.2863ms [CUDA memcpy DtoH] ==78544== API calls: Time(%) Time Calls Avg Min Max Name 46.85% 682.28ms 8 85.285ms 12.639us 682.03ms cudaStreamCreateWithFlags 39.83% 580.00ms 4 145.00ms 302ns 550.27ms cudaFree 9.82% 143.03ms 9 15.892ms 8.7090us 142.78ms cudaStreamCreate 1.23% 17.983ms 7 2.5690ms 23.210us 6.4563ms cudaMemcpy 1.23% 17.849ms 2 8.9247ms 8.4726ms 9.3768ms cudaStreamSynchronize 0.66% 9.5969ms 7 1.3710ms 288.43us 2.4279ms cudaHostAlloc 0.13% 1.9530ms 11 177.54us 7.6810us 591.06us cudaMalloc 0.07% 1.0424ms 8 130.30us 1.6970us 453.72us cudaGetDevice 0.04% 527.90us 40 13.197us 525ns 253.99us cudaEventCreateWithFlags 0.03% 435.73us 348 1.2520us 124ns 42.704us cuDeviceGetAttribute 0.03% 419.36us 1 419.36us 419.36us 419.36us cudaGetDeviceCount 0.02% 260.75us 2 130.38us 129.32us 131.43us cudaGetDeviceProperties 0.02% 222.32us 2 111.16us 106.94us 115.39us cudaLaunch 0.01% 214.06us 4 53.514us 28.586us 77.655us cuDeviceGetName 0.01% 115.45us 4 28.861us 9.8250us 44.526us cuDeviceTotalMem 0.01% 83.988us 4 20.997us 578ns 77.760us cudaSetDevice 0.00% 38.918us 1 38.918us 38.918us 38.918us cudaEventCreate 0.00% 34.573us 31 1.1150us 279ns 12.784us cudaDeviceGetAttribute 0.00% 17.767us 1 17.767us 17.767us 17.767us cudaProfilerStart 0.00% 15.228us 2 7.6140us 3.5460us 11.682us cudaConfigureCall 0.00% 14.536us 2 7.2680us 1.1490us 13.387us cudaGetLastError 0.00% 8.6080us 26 331ns 173ns 783ns cudaSetupArgument 0.00% 5.5470us 6 924ns 215ns 2.6780us cuDeviceGet 0.00% 5.4090us 6 901ns 328ns 3.3320us cuDeviceGetCount 0.00% 4.1770us 3 1.3920us 1.0630us 1.8300us cuDriverGetVersion 0.00% 3.4650us 3 1.1550us 1.0810us 1.2680us cuInit 0.00% 830ns 1 830ns 830ns 830ns cudaRuntimeGetVersion nvvp profiler ------------- For visual profiler **nvvp**, you can either import the output of :code:`nvprof –o ...` or run application through GUI. **Note: nvvp also support CPU profiling** (Click the box in nvvp to enable profile execution on CPU). .. image:: nvvp1.png :align: center :scale: 33% From the perspective of kernel functions, **nvvp** can even illustrate why does an operation take a long time? As shown in the following figure, kernel's block usage, register usage and shared memory usage from :code:`nvvp` allow us to fully utilize all warps on the GPU. .. image:: nvvp2.png :align: center :scale: 33% From the perspective of application, **nvvp** can give you some suggestions to address performance bottleneck. For instance, some advice in data movement and compute utilization from the below figure can guide you to tune performance. .. image:: nvvp3.png :align: center :scale: 33% .. image:: nvvp4.png :align: center :scale: 33% Profiling tips ============== - The **nvprof** and **nvvp** output is a very good place to start. - The timeline is a good place to go next. - Only dig deep into a kernel if it’s taking a significant amount of your time. - Where possible, try to match profiler output with theory. 1) For example, if I know I’m moving 1GB, and my kernel takes 10ms, I expect the profiler to report 100GB/s. 2) Discrepancies are likely to mean your application isn’t doing what you thought it was. - Know your hardware: If your GPU can do 6 TFLOPs, and you’re already doing 5.5 TFLOPs, you won’t go much faster! Profiling is a key step in optimization. Sometimes quite simple changes can lead to big improvements in performance. Your mileage may vary! Reference ========= Jeremy Appleyard, `GPU Profiling for Deep Learning `_, 2015