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

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Date:   Mon, 17 May 2021 16:10:58 +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> [2021-05-14 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?


-- 
Thanks and Regards
Srikar Dronamraju