linux-kernel - [PATCH v2 0/2] sched/nohz: disallow non-existent cores from nohz-full

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Date:   Mon, 21 Feb 2022 13:20:07 -0500
From:   Paul Gortmaker <paul.gortmaker@...driver.com>
To:     <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Peter Zijlstra <peterz@...radead.org>
CC:     Paul Gortmaker <paul.gortmaker@...driver.com>,
        Ingo Molnar <mingo@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH v2 0/2] sched/nohz: disallow non-existent cores from nohz-full

This is a rebase and retest of two fixes I'd sent earlier[1].

The rebase is required due to conflicts in my patch #1 and where Frederic updated
the unwind code in housekeeping_setup in his series[2] and that series is now
in sched/core of tip[3].

So this update is against a baseline of ed3b362d54f0 found in sched/core as
"sched/isolation: Split housekeeping cpumask per isolation features" in tip.

Changes amount to "return 0" ---> "goto out_free" and adding a nod to PaulM's
observation that nohz_full w/o a cpuset is coming someday into the commit log.

[1] https://lore.kernel.org/all/20211206145950.10927-1-paul.gortmaker@windriver.com/
[2] https://lore.kernel.org/all/20220207155910.527133-1-frederic@kernel.org/
[3] git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git

 ----- Original v1 text follows ----- 

A couple months back I sent a fix to reconcile rcu_nocbs= input
restrictions with nohz_full= input restrictions; with the latter being
more restrictive than the former.

However, in relaxing the nohz_full restrictions, I made it possible to
boot with a nohz_full= parameter that contains nothing but nonexistent
and not-possible cores - which will trigger a WARN.

This fixes the original reconcile commit by explicitly coding our
allowed values just like RCU does, and changes the WARN_ON to a
WARN_ON_ONCE, since it needlessly rendered the machine unusable.

---

Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Nicholas Piggin <npiggin@...il.com>
Cc: Paul E. McKenney <paulmck@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>

Paul Gortmaker (2):
  sched/isolation: really align nohz_full with rcu_nocbs
  tick/nohz: WARN_ON --> WARN_ON_ONCE to prevent console saturation

 kernel/sched/isolation.c | 11 +++++++++++
 kernel/time/tick-sched.c |  2 +-
 2 files changed, 12 insertions(+), 1 deletion(-)

-- 
2.17.1