linux-kernel - Re: [PATCH v6 0/2] Adjust NUMA imbalance for multiple LLCs

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Date:   Wed, 9 Feb 2022 10:38:28 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     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>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Gautham Shenoy <gautham.shenoy@....com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 0/2] Adjust NUMA imbalance for multiple LLCs

On Tue, Feb 08, 2022 at 09:43:32AM +0000, Mel Gorman wrote:
> Changelog sinve v5
> o Fix off-by-one error
> 
> Changelog since V4
> o Scale imbalance based on the top domain that prefers siblings
> o Keep allowed imbalance as 2 up to the point where LLCs can be overloaded
> 
> Changelog since V3
> o Calculate imb_numa_nr for multiple SD_NUMA domains
> o Restore behaviour where communicating pairs remain on the same node
> 
> 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.
> 
> The series addresses two problems -- inconsistent logic when allowing a
> NUMA imbalance and sub-optimal performance when there are many LLCs per
> NUMA node.
> 
>  include/linux/sched/topology.h |  1 +
>  kernel/sched/fair.c            | 30 ++++++++++---------
>  kernel/sched/topology.c        | 53 ++++++++++++++++++++++++++++++++++
>  3 files changed, 71 insertions(+), 13 deletions(-)

Thanks!