From: Peter Zijlstra <peterz@infradead.org>
To: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: mingo@kernel.org, vincent.guittot@linaro.org,
linux-kernel@vger.kernel.org, kprateek.nayak@amd.com,
juri.lelli@redhat.com, vschneid@redhat.com, tglx@linutronix.de,
dietmar.eggemann@arm.com, anna-maria@linutronix.de,
frederic@kernel.org, wangyang.guo@intel.com
Subject: Re: [PATCH v3 1/3] sched/fair: Move checking for nohz cpus after time check
Date: Thu, 8 Jan 2026 13:44:43 +0100 [thread overview]
Message-ID: <20260108124443.GA2490257@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20260107065125.669668-2-sshegde@linux.ibm.com>
On Wed, Jan 07, 2026 at 12:21:23PM +0530, Shrikanth Hegde wrote:
> NOHZ idle load balancer is kicked off only after time check. So move
> the atomic read after the time check to access it only when needed.
>
> When there are no idle CPUs(100% busy), even if the flag gets set to
> NOHZ_STATS_KICK | NOHZ_NEXT_KICK, find_new_ilb will fail and
> there will be no NOHZ idle balance. The current behaviour is retained.
>
> Note: This patch doesn't solve any cacheline overheads. No improvement
> in performance apart from saving a few cycles of atomic_read.
Note that atomic_read() == READ_ONCE() is just a regular load, but sure.
next prev parent reply other threads:[~2026-01-08 12:44 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-07 6:51 [PATCH v3 0/3] sched/fair: Improve nohz fields for large systems Shrikanth Hegde
2026-01-07 6:51 ` [PATCH v3 1/3] sched/fair: Move checking for nohz cpus after time check Shrikanth Hegde
2026-01-08 12:44 ` Peter Zijlstra [this message]
2026-01-09 15:14 ` Shrikanth Hegde
2026-01-07 6:51 ` [PATCH v3 2/3] sched/fair: Change likelyhood of nohz.nr_cpus Shrikanth Hegde
2026-01-07 6:51 ` [PATCH v3 3/3] sched/fair: Remove nohz.nr_cpus and use weight of cpumask instead Shrikanth Hegde
2026-01-09 14:44 ` Valentin Schneider
2026-01-09 15:15 ` Shrikanth Hegde
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