linux-kernel - [PATCH v5 0/2] Adjust NUMA imbalance for multiple LLCs

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Date:   Thu,  3 Feb 2022 14:46:50 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Peter Zijlstra <peterz@...radead.org>
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>,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH v5 0/2] Adjust NUMA imbalance for multiple LLCs

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(-)

-- 
2.31.1

Mel Gorman (2):
  sched/fair: Improve consistency of allowed NUMA balance calculations
  sched/fair: Adjust the allowed NUMA imbalance when SD_NUMA spans
    multiple LLCs

 include/linux/sched/topology.h |  1 +
 kernel/sched/fair.c            | 30 ++++++++++---------
 kernel/sched/topology.c        | 53 ++++++++++++++++++++++++++++++++++
 3 files changed, 71 insertions(+), 13 deletions(-)

-- 
2.31.1