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Add some notes on getting reproducible benchmark numbers on panfrost/panthor based SoCs. Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com> Reviewed-by: Iago Toral Quiroga <itoral@igalia.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38584>
71 lines
2.7 KiB
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71 lines
2.7 KiB
ReStructuredText
Benchmarking Panfrost
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=====================
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Obtaining reproducible benchmark timings can sometimes be tricky on Mali
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based SoCs. There are a number of things that can be done to make the timings
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more predictable.
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Make sure the device is actively cooled (to eliminate thermal throttling)
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-------------------------------------------------------------------------
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This isn't strictly speaking necessary, if you use low enough frequencies
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in the steps below, but it is recommended.
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Fix the GPU frequency
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---------------------
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If power management is allowed to vary the GPU frequency, this will lead to
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uncertainty in benchmark figures, particularly for shorter benchmark runs.
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On most systems, the GPU frequency can be set to a fixed value via a command
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like the following (run it as root, sudo alone won't allow the redirection):
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.. code-block:: sh
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cat /sys/devices/platform/fb000000.gpu/devfreq/fb000000.gpu/min_freq > /sys/devices/platform/fb000000.gpu/devfreq/fb000000.gpu/max_freq
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This forces the GPU to always use its minimum frequency. You could reverse
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`min_freq` and `max_freq` to fix it to its maximum frequency, if your system
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is adequately cooled.
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Fix the CPU frequency
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---------------------
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It is easy to overlook the role the CPU plays in driver performance. To set
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its frequency to a fixed value, install the `linux-cpupower` package and
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run something like:
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.. code-block:: sh
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sudo cpupower frequency-info
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sudo cpupower frequency-set -d 1.20
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sudo cpupower frequency-set -u 1.20
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sudo cpupower frequency-info
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Adjust the numbers based on what the board actually supports (seen in
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the first `frequency-info`. It is best to choose fairly low settings
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unless you're confident of the board's cooling.
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Pin the benchmark program to a particular core
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----------------------------------------------
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This is especially important on devices with a big.LITTLE architecture, where
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having the benchmark be scheduled on a different kind of core can drastically
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change the performance. But even without this, variations in cache residency
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and scheduling of kernel tasks can lead to changes in benchmark timing.
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Experience shows that using a little core for the benchmark program
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tends to give more reproducible results (probably because they have smaller
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caches, and also are less likely to be scheduled to by the kernel).
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However, forcing the benchmark to run on a little core could change the
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bottleneck from GPU to CPU, so watch out for that.
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Pinning a task to a particular core is done with the `taskset` command. An
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example for the Rock5b (rk3588) board is:
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.. code-block:: sh
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taskset 0x04 glmark2-es2-wayland
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Replace `0x04` with an appropriate mask for your board, and
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`glmark2-es2-wayland` with the benchmark program to be used.
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