linux-kernel - [PATCH v2 0/2] sched/fair: nohz.next

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Message-Id: <20210719103117.3624936-1-valentin.schneider@arm.com>
Date:   Mon, 19 Jul 2021 11:31:15 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>
Subject: [PATCH v2 0/2] sched/fair: nohz.next_balance vs newly-idle CPUs

Hi folks,

The single patch has grown a sibling, and a cover letter along with it.

This was caught up by our testing on an arm64 RB5 board - that's an 8 CPUs
DynamIQ SoC with 4 littles, 3 mediums and 1 big. It seems to rely more on NOHZ
balancing than our other boards being tested, which highlighted that not
including a newly-idle CPU into nohz.next_balance can cause issues (especially
when the other CPUs have had their balance_interval inflated by pinned tasks).

As suggested by Vincent, the approach here is to mimic what was done for
nohz.has_blocked, which gives us sane(ish) ordering guarantees.

Revisions
=========

v1 -> v2
++++++++

o Ditched the extra cpumasks and went with a sibling of nohz.has_blocked
  (Vincent) 

Cheers,
Valentin

Valentin Schneider (2):
  sched/fair: Add NOHZ balancer flag for nohz.next_balance updates
  sched/fair: Trigger nohz.next_balance updates when a CPU goes
    NOHZ-idle

 kernel/sched/fair.c  | 24 +++++++++++++++++++-----
 kernel/sched/sched.h |  8 +++++++-
 2 files changed, 26 insertions(+), 6 deletions(-)

-- 
2.25.1