linux-kernel - Re: [tip:sched/core] sched/fair: Remove #ifdefs from scale_rt

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Date:   Sat, 15 Sep 2018 13:46:57 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     mingo@...hat.com, viresh.kumar@...aro.org,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        vincent.guittot@...aro.org, hpa@...or.com
Cc:     linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/core] sched/fair: Remove #ifdefs from
 scale_rt_capacity()


* tip-bot for Vincent Guittot <tipbot@...or.com> wrote:

> Commit-ID:  2e62c4743adc4c7bfcbc1f45118fc7bec58cf30a
> Gitweb:     https://git.kernel.org/tip/2e62c4743adc4c7bfcbc1f45118fc7bec58cf30a
> Author:     Vincent Guittot <vincent.guittot@...aro.org>
> AuthorDate: Thu, 19 Jul 2018 14:00:06 +0200
> Committer:  Ingo Molnar <mingo@...nel.org>
> CommitDate: Wed, 25 Jul 2018 11:41:05 +0200
> 
> sched/fair: Remove #ifdefs from scale_rt_capacity()
> 
> Reuse cpu_util_irq() that has been defined for schedutil and set irq util
> to 0 when !CONFIG_IRQ_TIME_ACCOUNTING.
> 
> But the compiler is not able to optimize the sequence (at least with
> aarch64 GCC 7.2.1):
> 
> 	free *= (max - irq);
> 	free /= max;
> 
> when irq is fixed to 0
> 
> Add a new inline function scale_irq_capacity() that will scale utilization
> when irq is accounted. Reuse this funciton in schedutil which applies
> similar formula.
> 
> Suggested-by: Ingo Molnar <mingo@...hat.com>
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: rjw@...ysocki.net
> Link: http://lkml.kernel.org/r/1532001606-6689-1-git-send-email-vincent.guittot@linaro.org
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> ---
>  kernel/sched/core.c              |  2 +-
>  kernel/sched/cpufreq_schedutil.c |  3 +--
>  kernel/sched/fair.c              | 13 +++----------
>  kernel/sched/sched.h             | 20 ++++++++++++++++++--
>  4 files changed, 23 insertions(+), 15 deletions(-)

This commit introduced a build warning in the SMP=n case, could we please fix that? (Probably 
the best to maintain variant would be to mark it as __maybe_unused.)

Also, while at it, there's a number of other places that use this pattern:

> -#if defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)
> +#ifdef HAVE_SCHED_AVG_IRQ

Could we convert those to HAVE_SCHED_AVG_IRQ as well?

dagon:~/tip> git grep 'defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)' kernel/sched/
kernel/sched/core.c:#if defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)
kernel/sched/fair.c:#if defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)
kernel/sched/pelt.c:#if defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)
kernel/sched/pelt.h:#if defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)
kernel/sched/sched.h:#if defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)

Thanks,

	Ingo