Pratik Basyal
ed05c00103
* Formatting issue in code block and TOC fixed * Performance model reverted
50 lines
2.6 KiB
ReStructuredText
50 lines
2.6 KiB
ReStructuredText
.. meta::
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:description: ROCm Compute Profiler: using PC sampling
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:keywords: ROCm Compute Profiler, PC sampling
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********************************************
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Using PC sampling in ROCm Compute Profiler
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********************************************
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Program Counter (PC) sampling service for GPU profiling is a profiling technique that periodically samples the program counter during the GPU kernel execution to understand code execution patterns and hotspots.
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ROCm Compute Profiler supports Host Trap PC sampling and Stochastic (Hardware-Based) PC sampling.
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Host Trap PC sampling is enabled for AMD Instinct MI200 series and later
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accelerators. Stochastic (hardware-based) PC sampling is enabled for
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AMD Instinct MI300 series and later accelerators. Stochastic PC sampling provides additional information that tells whether a sampled wave issued an instruction for a particular PC. It also provides the reason
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for not issuing the instruction (stall reason). This type of information is
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particularly useful for understanding stalls during the kernel execution. The PC sampling can be used with profiling and analysis options.
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---------------------
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Profiling options
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---------------------
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For using profiling options for PC sampling the configuration needed are:
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* ``--pc-sampling-method``: Should be either ``stochastic`` or ``host_trap``
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* ``--pc-sampling-interval``: For stochastic sampling, the interval is in cycles. The finest granularity is 1 cycle. For host_trap sampling, the interval is in microsecond (DEFAULT: 1048576). The interval should be the power of 2. You are recommended to try to starting from 1048576, and lowering until reaching 65536.
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**Sample command:**
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.. code-block:: shell
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$ rocprof-compute profile -n pc_test -b 21 --no-roof --pc-sampling-method stochastic --pc-sampling-interval 1048576 -VVV -- target_app
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-----------------------
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Analysis options
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-----------------------
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For using analysis options for PC sampling the configuration needed are:
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* ``--pc-sampling-sorting-type``: ``offset`` or ``count``. The default option is ``offset``. ``offset`` is an assembly instruction offset in the code object.
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**Sample command:**
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.. code-block:: shell
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$ rocprof-compute analyze -p workloads/pc_test/MI300A_A1/ -b 21 -k 0 --pc-sampling-sorting-type offset
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.. note::
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* PC sampling feature is currently in BETA version. To enable PC sampling, you have to explicitly enable it with block index 21.
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* To associate PC sampling info back to HIP source code, you need to build the profiling target app with ``-g`` to keep the symbols. Otherwise, PC sampling info would be only associated with assembly lines.
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