[Intel-gfx] [RFC] GPU-bound energy efficiency improvements for the intel_pstate driver (v2.99)

Peter Zijlstra peterz at infradead.org
Mon May 11 10:57:01 UTC 2020

On Mon, Apr 27, 2020 at 08:22:47PM -0700, Francisco Jerez wrote:
> This addresses the technical concerns people brought up about my
> previous v2 revision of this series.  Other than a few bug fixes, the
> only major change relative to v2 is that the controller is now exposed
> as a new CPUFREQ generic governor as requested by Rafael (named
> "adaptive" in this RFC though other naming suggestions are welcome).
> Main reason for calling this v2.99 rather than v3 is that I haven't
> yet addressed all the documentation requests from the v2 thread --
> Will spend some time doing that as soon as I have an ACK (ideally from
> Rafael) that things are moving in the right direction.
> You can also find this series along with the WIP code for non-HWP
> platforms in this branch:
> https://github.com/curro/linux/tree/intel_pstate-vlp-v2.99
> Thanks!
> [PATCHv2.99 01/11] PM: QoS: Add CPU_SCALING_RESPONSE global PM QoS limit.
> [PATCHv2.99 02/11] drm/i915: Adjust PM QoS scaling response frequency based on GPU load.
> [PATCHv2.99 03/11] OPTIONAL: drm/i915: Expose PM QoS control parameters via debugfs.
> [PATCHv2.99 04/11] cpufreq: Define ADAPTIVE frequency governor policy.
> [PATCHv2.99 05/11] cpufreq: intel_pstate: Reorder intel_pstate_clear_update_util_hook() and intel_pstate_set_update_util_hook().
> [PATCHv2.99 06/11] cpufreq: intel_pstate: Call intel_pstate_set_update_util_hook() once from the setpolicy hook.
> [PATCHv2.99 07/11] cpufreq: intel_pstate: Implement VLP controller statistics and target range calculation.
> [PATCHv2.99 08/11] cpufreq: intel_pstate: Implement VLP controller for HWP parts.
> [PATCHv2.99 09/11] cpufreq: intel_pstate: Enable VLP controller based on ACPI FADT profile and CPUID.
> [PATCHv2.99 10/11] OPTIONAL: cpufreq: intel_pstate: Add tracing of VLP controller status.
> [PATCHv2.99 11/11] OPTIONAL: cpufreq: intel_pstate: Expose VLP controller parameters via debugfs.

What I'm missing is an explanation for why this isn't using the
infrastructure that was build for these kinds of things? The thermal
framework, was AFAIU, supposed to help with these things, and the IPA
thing in particular is used by ARM to do exactly this GPU/CPU power
budget thing.

If thermal/IPA is found wanting, why aren't we improving that?

How much of that ADAPTIVE crud is actually intel_pstate specific? On a
(really) quick read it appears to me that much of the controller bits
there can be applied more generic, and thus should not be part of any
one governor.

Specifically, I want to use sched_util as cpufreq governor and use the
intel_pstate as a passive driver.

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