linux-kernel - Re: [PATCH v2 6/8] sched/idle: Move busy

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Date:   Mon, 17 May 2021 18:27:27 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Aubrey Li <aubrey.li@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Rik van Riel <riel@...riel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Valentin Schneider <valentin.schneider@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
        Parth Shah <parth@...ux.ibm.com>
Subject: Re: [PATCH v2 6/8] sched/idle: Move busy_cpu accounting to idle
 callback

* Aubrey Li <aubrey.li@...ux.intel.com> [2021-05-17 20:48:46]:

> On 5/17/21 6:40 PM, Srikar Dronamraju wrote:
> > * Aubrey Li <aubrey.li@...ux.intel.com> [2021-05-14 12:11:50]:
> > 
> >> On 5/13/21 3:31 PM, Srikar Dronamraju wrote:
> >>> * Aubrey Li <aubrey.li@...ux.intel.com> [2021-05-12 16:08:24]:
> >>>> On 5/7/21 12:45 AM, Srikar Dronamraju wrote:
> > 
> > <snip>
> > 
> >>>> Also, for those frequent context-switching tasks with very short idle,
> >>>> it's expensive for scheduler to mark idle/busy every time, that's why
> >>>> my patch only marks idle every time and marks busy ratelimited in
> >>>> scheduler tick.
> >>>>
> >>>
> >>> I have tried few tasks with very short idle times and updating nr_busy
> >>> everytime, doesnt seem to be impacting. Infact, it seems to help in picking
> >>> the idler-llc more often.
> >>>
> >>
> >> How many CPUs in your LLC?
> > 
> > I have tried with X86, 48 CPUs, 2 nodes, each having 24 CPUs in LLC
> > +
> > POWER10, Multiple CPUs with 4 CPUs in LLC
> > +
> > POWER9, Multiple CPUs with 8 CPUs in LLC
> > 
> >>
> >> This is a system with 192 CPUs, 4 nodes and each node has 48 CPUs in LLC
> >> domain.
> >>
> > 
> > Okay,
> > 
> >> It looks like for netperf both TCP and UDP cases have the notable change
> >> under 2 x overcommit, it may be not interesting though.
> >>
> >>
> > 
> > I believe the extra load on this 24 core LLC could be because we may end up
> > trying to set the idle-core, even when there is no idle core available.
> > 
> > If possible, can you please give a try with v3 with the call to
> > set_next_idle_core commented out?
> > 
> > 
> 
> v3 seems not be applicable on tip/sched/core 915a2bc3c6b7?

I had applied on top of 2ea46c6fc9452ac100ad907b051d797225847e33
which was tag: sched-core-2021-04-28

The only conflict you get on today's tip is Gautham's one line patch.
Gautham's patch replaced 'this' with 'target'.

The 2nd patch does away with that line

-- 
Thanks and Regards
Srikar Dronamraju