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

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Date:   Tue, 24 Oct 2023 14:10:27 +0800
From:   Chen Yu <yu.c.chen@...el.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
CC:     Dietmar Eggemann <dietmar.eggemann@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        <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>,
        "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 2023-10-23 at 11:04:49 -0400, Mathieu Desnoyers wrote:
> On 2023-10-23 10:11, Dietmar Eggemann wrote:
> > On 19/10/2023 18:05, Mathieu Desnoyers wrote:
> 
> [...]
> > > +static unsigned long scale_rt_capacity(int cpu);
> > > +
> > > +/*
> > > + * Returns true if adding the task utilization to the estimated
> > > + * utilization of the runnable tasks on @cpu does not exceed the
> > > + * capacity of @cpu.
> > > + *
> > > + * This considers only the utilization of _runnable_ tasks on the @cpu
> > > + * runqueue, excluding blocked and sleeping tasks. This is achieved by
> > > + * using the runqueue util_est.enqueued.
> > > + */
> > > +static inline bool task_fits_remaining_cpu_capacity(unsigned long task_util,
> > > +						    int cpu)
> > 
> > Or like find_energy_efficient_cpu() (feec(), used in
> > Energy-Aware-Scheduling (EAS)) which uses cpu_util(cpu, p, cpu, 0) to get:
> > 
> >    max(util_avg(CPU + p), util_est(CPU + p))
> 
> I've tried using cpu_util(), but unfortunately anything that considers
> blocked/sleeping tasks in its utilization total does not work for my
> use-case.
> 
> From cpu_util():
> 
>  * CPU utilization is the sum of running time of runnable tasks plus the
>  * recent utilization of currently non-runnable tasks on that CPU.
>

I thought cpu_util() indicates the utilization decay sum of task that was once
"running" on this CPU, but will not sum up the "util/load" of the blocked/sleeping
task?

accumulate_sum()
    /* only the running task's util will be sum up */
    if (running)
       sa->util_sum += contrib << SCHED_CAPACITY_SHIFT;

WRITE_ONCE(sa->util_avg, sa->util_sum / divider);

thanks,
Chenyu