linux-kernel - Re: [PATCH] sched/debug: Fix requested task uclamp values shown in procfs

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Date:   Mon, 11 May 2020 07:25:47 +0530
From:   Pavan Kondeti <pkondeti@...eaurora.org>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Qais Yousef <qais.yousef@....com>
Subject: Re: [PATCH] sched/debug: Fix requested task uclamp values shown in
 procfs

On Sun, May 10, 2020 at 05:16:28PM +0100, Valentin Schneider wrote:
> 
> On 10/05/20 13:56, Pavankumar Kondeti wrote:
> > The intention of commit 96e74ebf8d59 ("sched/debug: Add task uclamp
> > values to SCHED_DEBUG procfs") was to print requested and effective
> > task uclamp values. The requested values printed are read from p->uclamp,
> > which holds the last effective values. Fix this by printing the values
> > from p->uclamp_req.
> >
> > Fixes: 96e74ebf8d59 ("sched/debug: Add task uclamp values to SCHED_DEBUG procfs")
> > Signed-off-by: Pavankumar Kondeti <pkondeti@...eaurora.org>
> 
> Argh, Qais pointed this out to me ~ a week ago, and I left this in my todo
> stack. I goofed up, sorry!
> 
> As Pavan points out, p->uclamp[foo] is just a cache of uclamp_eff_value(p,
> foo) from the last time p was enqueued and runnable - what we are
> interested in is indeed comparing this with the *requested* value.
> 
> I wanted to send an example along with a patch, I guess that's the kick I
> needed!
> 
> 
> My setup is a busy loop, its per-task clamps are set to (256, 768) via
> sched_setattr(), and it's shoved in a cpu cgroup with uclamp settings of
> (50%, 50%)
> 
> On the current master (e99332e7b4cd ("gcc-10: mark more functions __init to
> avoid section mismatch warnings")), this gives me:
> 
>   $ uclamp-get $PID # via sched_getattr()
>   uclamp.min=256 uclamp.max=768
> 
>   $ cat /proc/$PID/sched | grep uclamp
>   uclamp.min                                   :                  256
>   uclamp.max                                   :                  512
>   effective uclamp.min                         :                  256
>   effective uclamp.max                         :                  512
> 
> With Pavan's patch, I get:
> 
>   $ uclamp-get $PID # via sched_getattr()
>   uclamp.min=256 uclamp.max=768
> 
>   $ cat /proc/$PID/sched | grep uclamp
>   uclamp.min                                   :                  256
>   uclamp.max                                   :                  768
>   effective uclamp.min                         :                  256
>   effective uclamp.max                         :                  512
> 
> 
> Minor print nit below, otherwise:
> Tested-and-reviewed-by: Valentin Schneider <valentin.schneider@....com>
> 
> Peter/Ingo, any chance this can go to sched/urgent? I know it's a debug
> interface, but I'd rather have it land in a shape that makes sense. Again,
> apologies for the goof.
> 
> > ---
> >  kernel/sched/debug.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> > index a562df5..239970b 100644
> > --- a/kernel/sched/debug.c
> > +++ b/kernel/sched/debug.c
> > @@ -948,8 +948,8 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns,
> >       P(se.avg.util_est.enqueued);
> >  #endif
> >  #ifdef CONFIG_UCLAMP_TASK
> > -	__PS("uclamp.min", p->uclamp[UCLAMP_MIN].value);
> > -	__PS("uclamp.max", p->uclamp[UCLAMP_MAX].value);
> > +	__PS("uclamp.min", p->uclamp_req[UCLAMP_MIN].value);
> > +	__PS("uclamp.max", p->uclamp_req[UCLAMP_MAX].value);
> 
> While we're at it, I'd prepend this with "requested".
> 
> >       __PS("effective uclamp.min", uclamp_eff_value(p, UCLAMP_MIN));
> >       __PS("effective uclamp.max", uclamp_eff_value(p, UCLAMP_MAX));
> >  #endif

Thanks Valentin for taking a look. I have added "requested" prefix and sent
the patch.

Thanks,
Pavan

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