cpufreq/amd-pstate: Set the initial min_freq to lowest_nonlinear_freq

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According to the AMD architectural programmer's manual volume 2 [1], in
section "17.6.4.1 CPPC_CAPABILITY_1" lowest_nonlinear_perf is described
as "Reports the most energy efficient performance level (in terms of
performance per watt). Above this threshold, lower performance levels
generally result in increased energy efficiency. Reducing performance
below this threshold does not result in total energy savings for a given
computation, although it reduces instantaneous power consumption". So
lowest_nonlinear_perf is the most power efficient performance level, and
going below that would lead to a worse performance/watt.

Also, setting the minimum frequency to lowest_nonlinear_freq (instead of
lowest_freq) allows the CPU to idle at a higher frequency which leads
to more time being spent in a deeper idle state (as trivial idle tasks
are completed sooner). This has shown a power benefit in some systems,
in other systems, power consumption has increased but so has the
throughput/watt.

Modify the initial policy_data->min set by cpufreq-core to
lowest_nonlinear_freq, in the ->verify() callback. Also set the
cpudata->req[0] to FREQ_QOS_MIN_DEFAULT_VALUE (i.e. 0), so that it also
gets overriden by the check in verify function.

Link: https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/programmer-references/24593.pdf [1]

Signed-off-by: Dhananjay Ugwekar <Dhananjay.Ugwekar@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://lore.kernel.org/r/20241017053927.25285-3-Dhananjay.Ugwekar@amd.com
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>

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Dhananjay Ugwekar 2024-10-17 05:39:30 +00:00 • committed by Mario Limonciello

parent 205cb215d0

commit 5d9a354cf8

1 changed files with 20 additions and 1 deletions

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drivers/cpufreq/amd-pstate.c

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