linux-kernel - Re: [RESEND PATCH v2 1/2] sched/rt: add utilization tracking

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Date:   Mon, 7 Aug 2017 18:44:55 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org, rjw@...ysocki.net,
        juri.lelli@....com, dietmar.eggemann@....com,
        Morten.Rasmussen@....com, viresh.kumar@...aro.org
Subject: Re: [RESEND PATCH v2 1/2] sched/rt: add utilization tracking

On Fri, Aug 04, 2017 at 03:40:21PM +0200, Vincent Guittot wrote:

> There were several comments on v1:
> - As raised by Peter for v1, if IRQ time is taken into account in
>   rt_avg, it will not be accounted in rq->clock_task. This means that cfs
>   utilization is not affected by some extra contributions or decays
>   because of IRQ.  

Right.

> - Regading the sync of rt and cfs utilization, both cfs and rt use the same
>   rq->clock_task. Then, we have the same issue than cfs regarding blocked value.
>   The utilization of idle cfs/rt rqs are not updated regularly but only when a
>   load_balance is triggered (more precisely a call to update_blocked_average).
>   I'd like to fix this issue for both cfs and rt with a separate patch that
>   will ensure that utilization (and load) are updated regularly even for
>   idle CPUs

Yeah, that needs help.

> - One last open question is the location of rt utilization function in fair.c
>   file. PELT related funtions should probably move in a dedicated pelt.c file.
>   This would also help to address one comment about having a place to update
>   metrics of NOHZ idle CPUs. Thought ?

Probably, but I have a bunch of patches lined up changing that code, so
lets not do that now.

In any case, would something like the attached patches make sense? It
completely replaces rt_avg with separate IRQ,RT and DL tracking.



View attachment "peterz-dl-util.patch" of type "text/x-diff" (3232 bytes)

View attachment "peterz-irq-util.patch" of type "text/x-diff" (2557 bytes)

View attachment "peterz-remove-rt_avg.patch" of type "text/x-diff" (7653 bytes)