linux-kernel - Re: [RFC PATCH v2 1/2] sched/fair: Introduce UTIL_FITS

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Message-ID: <20231025075646.GB37471@noisy.programming.kicks-ass.net>
Date:   Wed, 25 Oct 2023 09:56:46 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Swapnil Sapkal <Swapnil.Sapkal@....com>,
        Aaron Lu <aaron.lu@...el.com>, Chen Yu <yu.c.chen@...el.com>,
        Tim Chen <tim.c.chen@...el.com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        "Gautham R . Shenoy" <gautham.shenoy@....com>, x86@...nel.org
Subject: Re: [RFC PATCH v2 1/2] sched/fair: Introduce UTIL_FITS_CAPACITY
 feature (v2)

On Thu, Oct 19, 2023 at 12:05:22PM -0400, Mathieu Desnoyers wrote:

> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index e93e006a942b..463e75084aed 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -2090,6 +2090,11 @@ static const_debug __maybe_unused unsigned int sysctl_sched_features =
>  
>  #endif /* SCHED_DEBUG */
>  
> +static __always_inline bool sched_util_fits_capacity_active(void)
> +{
> +	return sched_feat(UTIL_EST) && sched_feat(UTIL_FITS_CAPACITY);
> +}

This generates pretty terrible code; it cannot collapse this into a
single branch. And since sched_feat is at best a debug interface for
people who knows wtf they're doing, just make this UTIL_FITS_CAPACITY
with a comment or so.