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Favorite nsight systems profiling commands for Pytorch scripts
# This isn't supposed to run as a bash script, i named it with ".sh" for syntax highlighting.
# https://developer.nvidia.com/nsight-systems
# https://docs.nvidia.com/nsight-systems/profiling/index.html
# My preferred nsys (command line executable used to create profiles) commands
#
# In your script, write
# torch.cuda.nvtx.range_push("region name")
# ...
# torch.cuda.nvtx.range_pop()
# around suspected hotspot regions for easy identification on the timeline.
#
# Dummy/warmup iterations prior to the region you want to profile are highly
# recommended to get caching allocator/cuda context initialization out of the way.
#
# Copy paste the desired command and run it for your app. It will produce a .qdrep file.
# Run the "nsight-sys" GUI executable and File->Open the .qdrep file.
# If you're making the profile locally on your desktop, you may not need nsys at all, you can do
# the whole workflow (create and view profile) through the GUI, but if your job runs remotely on
# a cluster node, I prefer to create .qdrep profiles with nsys remotely, copy them back to my desktop,
# then open them in nsight-sys.
# Typical use (collects GPU timeline, Cuda and OS calls on the CPU timeline, but no CPU stack traces)
nsys profile -w true -t cuda,nvtx,osrt,cudnn,cublas -s none -o nsight_report -f true -x true python script.py args...
# Adds CPU backtraces that will show when you mouse over a long call or small orange tick (sample) on the CPU timeline:
nsys profile -w true -t cuda,nvtx,osrt,cudnn,cublas -s cpu -o nsight_report -f true --cudabacktrace=true --cudabacktrace-threshold=10000 --osrt-threshold=10000 -x true python script.py args...
# Focused profiling, profiles only a target region
# (your app must call torch.cuda.cudart().cudaProfilerStart()/Stop() at the start/end of the target region)
nsys profile -w true -t cuda,nvtx,osrt,cudnn,cublas -s cpu -o nsight_report -f true --capture-range=cudaProfilerApi --stop-on-range-end=true --cudabacktrace=true --cudabacktrace-threshold=10000 --osrt-threshold=10000 -x true python script.py args...
# if appname creates child processes, nsys WILL profile those as well. They will show up as separate processes with
# separate timelines when you open the profile in nsight-sys
# Breakdown of options:
nsys profile
-w true # Don't suppress app's console output.
-t cuda,nvtx,osrt,cudnn,cublas # Instrument, and show timeline bubbles for, cuda api calls, nvtx ranges,
# os runtime functions, cudnn library calls, and cublas library calls.
# These options do not require -s cpu nor do they silently enable -s cpu.
-s cpu # Sample the cpu stack periodically. Stack samples show up as little tickmarks on the cpu timeline.
# Last time i checked they were orange, but still easy to miss.
# Mouse over them to show the backtrace at that point.
# -s cpu can increase cpu overhead substantially (I've seen 2X or more) so be aware of that distortion.
# -s none disables cpu sampling. Without cpu sampling, the profiling overhead is reduced.
# Use -s none if you want the timeline to better represent a production job (api calls and kernels will
# still appear on the profile, but profiling them doesn't distort the timeline nearly as much).
-o nsight_report # output file
-f true # overwrite existing output file
--capture-range=cudaProfilerApi # Only start profiling when the app calls cudaProfilerStart...
--stop-on-range-end=true # ...and end profiling when the app calls cudaProfilerStop.
--cudabacktrace=true # Collect a cpu stack sample for cuda api calls whose runtime exceeds some threshold.
# When you mouse over a long-running api call on the timeline, a backtrace will
# appear, and you can identify which of your functions invoked it.
# I really like this feature.
# Requires -s cpu.
--cudabacktrace-threshold=10000 # Threshold (in nanosec) that determines how long a cuda api call
# must run to trigger a backtrace. 10 microsec is a reasonable value
# (most kernel launches should take less than 10 microsec) but you
# should retune if you see a particular api call you'd like to investigate.
# Requires --cudabacktrace=true and -s cpu.
--osrt-threshold=10000 # Threshold (in nanosec) that determines how long an os runtime call (eg sleep)
# must run to trigger a backtrace.
# Backtrace collection for os runtime calls that exceed this threshold should
# occur by default if -s cpu is enabled.
-x true # Quit the profiler when the app exits.
python script.py args...
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