linux-kernel - Re: [PATCH 2/2] sched/fair: Adjust the allowed NUMA imbalance when SD

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Date:   Mon, 14 Feb 2022 15:57:07 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Mike Galbraith <efault@....de>,
        Gautham Shenoy <gautham.shenoy@....com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] sched/fair: Adjust the allowed NUMA imbalance when
 SD_NUMA spans multiple LLCs

* Mel Gorman <mgorman@...hsingularity.net> [2022-02-08 09:43:34]:

> Commit 7d2b5dd0bcc4 ("sched/numa: Allow a floating imbalance between NUMA
> nodes") allowed an imbalance between NUMA nodes such that communicating
> tasks would not be pulled apart by the load balancer. This works fine when
> there is a 1:1 relationship between LLC and node but can be suboptimal
> for multiple LLCs if independent tasks prematurely use CPUs sharing cache.
> 
> Zen* has multiple LLCs per node with local memory channels and due to
> the allowed imbalance, it's far harder to tune some workloads to run
> optimally than it is on hardware that has 1 LLC per node. This patch
> allows an imbalance to exist up to the point where LLCs should be balanced
> between nodes.
> 
> On a Zen3 machine running STREAM parallelised with OMP to have on instance
> per LLC the results and without binding, the results are
> 
>                             5.17.0-rc0             5.17.0-rc0
> 

Looks good to me.

Reviewed-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>

-- 
Thanks and Regards
Srikar Dronamraju