linux-kernel - Re: [PATCH v3 4/5] sched: Rename arch_update_thermal_pressure into arch_update_hw

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Date: Tue, 9 Jan 2024 14:33:00 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: linux@...linux.org.uk, catalin.marinas@....com, will@...nel.org, 
	sudeep.holla@....com, rafael@...nel.org, viresh.kumar@...aro.org, 
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Subject: Re: [PATCH v3 4/5] sched: Rename arch_update_thermal_pressure into arch_update_hw_pressure

On Tue, 9 Jan 2024 at 12:56, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>
> On 08/01/2024 14:48, Vincent Guittot wrote:
> > Now that cpufreq provides a pressure value to the scheduler, rename
>
> I.e. that thermal (e.g. IPA governor) switches from average
> (rq->avg_(thermal/hw).load_avg) (1) to instantenous (cpu_pressure) (2).
> I rememeber a related dicussion during LPC 2018 :-)
>
> > arch_update_thermal_pressure into HW pressure to reflect that it returns
> > a pressure applied by HW (i.e. with a high frequency change) and not
> > always related to thermal mitigation but also generated by max current
> > limitation as an example. Such high frequency signal needs filtering to be
> > smoothed and provide an value that reflects the average available capacity
> > into the scheduler time scale.
>
> So 'drivers/cpufreq/qcom-cpufreq-hw.c' is the only user of (1) right
> now. Are we expecting more users here? If this stays the only user,
> maybe it can do the averages by itself and we can completely switch to (2)?

Yes I expect more users for this high frequency change which is
typically 1ms and below. And I prefer to keep PELT averaging
calculation inside scheduler instead of letting driver doing their own
averaging which will be most of the time not aligned with what
scheduler wants

>
> [...]
>