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This commit adds two new configuration options: igpu_desiredgov and
igpu_power_threshold which allow for a different CPU governor when the
Intel integrated GPU is under load. This currently only applies to
Intel integrated GPUs and not AMD APUs because it uses the Intel RAPL
infrastructure for getting power information. If on a platform that
without an Intel integrated GPU or where the kernel does not support
RAPL, the new options will be ignored and it will fall back to the old
behavior.
One of the core principals of gamemoded to date has been that, when
playing a game, we want to use the "performance" CPU governor to
increase CPU performance and prevent CPU-limiting. However, when the
integrated GPU is under load, this can be counter-productive because the
CPU and GPU share a thermal and power budget. By throwing the CPU
governor to "performance" game mode currently makes the CPU frequency
management far too aggressive and it burns more power than needed. With
a discrete GPU, this is fine because the worst that happens is a bit
more fan noise. With an integrated GPU, however, the additional power
being burned by the CPU is power not available to the GPU and this can
cause the GPU to clock down and lead to significantly worse performance.
By using the "powersave" governor instead of the "performance" governor
while the integrated GPU is under load, we can save power on the CPU
side which lets the GPU clock up higher. On my Razer Blade Stealth 13
with an i7-1065G7, this improves the performance of "Shadow of the Tomb
Raider" by around 25-30% according to its internal benchmark mode.
