linux-kernel - Re: [RFC PATCH] sched/fair: update the vruntime to be max vruntime when yield

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Message-ID: <CAKfTPtBMPV_cLck8yTW1hLEKXX6_FFgbq76UK1w4cxtvoUF+Bg@mail.gmail.com>
Date:   Wed, 1 Mar 2023 14:29:59 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Xuewen Yan <xuewen.yan94@...il.com>,
        Qais Yousef <qyousef@...alina.io>,
        Peter Zijlstra <peterz@...radead.org>,
        Xuewen Yan <xuewen.yan@...soc.com>, mingo@...hat.com,
        juri.lelli@...hat.com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org, ke.wang@...soc.com,
        zhaoyang.huang@...soc.com
Subject: Re: [RFC PATCH] sched/fair: update the vruntime to be max vruntime
 when yield

On Wed, 1 Mar 2023 at 12:23, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>
> Hi Xuewen,
>
> On 01/03/2023 09:20, Xuewen Yan wrote:
> > On Wed, Mar 1, 2023 at 4:09 PM Vincent Guittot
> > <vincent.guittot@...aro.org> wrote:
> >>
> >> On Wed, 1 Mar 2023 at 08:30, Xuewen Yan <xuewen.yan94@...il.com> wrote:
> >>>
> >>> Hi Vincent
> >>>
> >>> I noticed the following patch:
> >>> https://lore.kernel.org/lkml/20230209193107.1432770-1-rkagan@amazon.de/
> >>> And I notice the V2 had merged to mainline:
> >>> https://lore.kernel.org/all/20230130122216.3555094-1-rkagan@amazon.de/T/#u
> >>>
> >>> The patch fixed the inversing of the vruntime comparison, and I see
> >>> that in my case, there also are some vruntime is inverted.
> >>> Do you think which patch will work for our scenario? I would be very
> >>> grateful if you could give us some advice.
> >>> I would try this patch in our tree.
> >>
> >> By default use the one that is merged; The difference is mainly a
> >> matter of time range. Also be aware that the case of newly migrated
> >> task is not fully covered by both patches.
> >
> > Okay, Thank you very much!
> >
> >>
> >> This patch fixes a problem with long sleeping entity in the presence
> >> of low weight and always running entities. This doesn't seem to be
> >> aligned with the description of your use case
> >
> > Thanks for the clarification! We would try it first to see whether it
> > could resolve our problem.
>
> Can you not run Vincent's rt-app example on your device and then report
> `cat /sys/kernel/debug/sched/debug` of the CPU?
>
> # rt-app /root/rt-app/cfs_yield.json
>
> # cat /sys/kernel/debug/sched/debug
> ...
> cpu#2
>   .nr_running                    : 4
>   ...
>   .curr->pid                     : 2121
>   ...
>
> cfs_rq[2]:/autogroup-15
>   .exec_clock                    : 0.000000
>   .MIN_vruntime                  : 32428.281204
>   .min_vruntime                  : 32428.281204
>   .max_vruntime                  : 32434.997784
>   ...
>   .nr_running                    : 4
>   .h_nr_running                  : 4
>
> ...
>
>  S            task   PID         tree-key  switches  prio     wait-time             sum-exec        sum-sleep
> -------------------------------------------------------------------------------------------------------------
>  S         cpuhp/2    22      1304.405864        13   120         0.000000         0.270000         0.000000         0.000000 0 0 /
>  S     migration/2    23         0.000000         8     0         0.000000         7.460940         0.000000         0.000000 0 0 /
>  S     ksoftirqd/2    24    137721.092326        46   120         0.000000         1.821880         0.000000         0.000000 0 0 /
>  I    kworker/2:0H    26      2116.827393         4   100         0.000000         0.057220         0.000000         0.000000 0 0 /
>  I     kworker/2:1    45    204539.183593       322   120         0.000000       447.975440         0.000000         0.000000 0 0 /
>  I     kworker/2:3    80      1778.668364        33   120         0.000000        16.237320         0.000000         0.000000 0 0 /
>  I    kworker/2:1H   239    199388.093936        74   100         0.000000         1.892300         0.000000         0.000000 0 0 /
>  R         taskA-0  2120     32428.281204       582   120         0.000000      1109.911280         0.000000         0.000000 0 0 /autogroup-15
> >R         taskB-1  2121     32430.693304       265   120         0.000000      1103.527660         0.000000         0.000000 0 0 /autogroup-15
>  R         taskB-2  2122     32432.137084       264   120         0.000000      1105.006760         0.000000         0.000000 0 0 /autogroup-15
>  R         taskB-3  2123     32434.997784       282   120         0.000000      1115.965120         0.000000         0.000000 0 0 /autogroup-15
>
> ...
>
> Not sure how Vincent's rt-app file looks like exactly but I crafted
> something quick here:

it was quite similar to yours below. I have just stopped to call yield
after few seconds to see if the behavior changed

>
> {
>         "tasks" : {
>                 "taskA" : {
>                         "cpus" : [2],
>                         "yield" : "taskA",
>                         "run" : 1000
>                 },
>                 "taskB" : {
>                         "instance" : 3,
>                         "cpus" : [2],
>                         "run" : 1000000
>                 }
>         },
>         "global" : {
>                 "calibration" : 156,
>                 "default_policy" : "SCHED_OTHER",
>                 "duration" : 20
>         }
> }
>
> [...]