From: Peter Zijlstra <peterz@infradead.org>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Christian Loehle <christian.loehle@arm.com>,
Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Valentin Schneider <vschneid@redhat.com>,
K Prateek Nayak <kprateek.nayak@amd.com>,
Beata Michalska <beata.michalska@arm.com>,
Elif Topuz <elif.topuz@arm.com>,
"Rafael J . Wysocki" <rafael@kernel.org>,
Daniel Lezcano <daniel.lezcano@kernel.org>,
Shubhang Kaushik <sh@gentwo.org>,
Christoph Lameter <cl@gentwo.org>,
Huang Shijie <shijie@os.amperecomputing.com>,
linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org
Subject: Re: [PATCH v2 2/2] sched/fair: Randomize equally shallow slow-path candidates
Date: Fri, 18 Sep 2026 13:43:17 +0200 [thread overview]
Message-ID: <20260918114317.GO776954@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <CAKfTPtBft2pVrsZQGJu0UBjuqaGJ2ViE9N6YExLvBnpgEXDvag@mail.gmail.com>
On Thu, Sep 17, 2026 at 06:06:42PM +0200, Vincent Guittot wrote:
> On Thu, 17 Sept 2026 at 17:41, Christian Loehle
> <christian.loehle@arm.com> wrote:
> >
> > Picking the first eligible idle CPU leaves a scan-order bias. Concurrent
> > slow-path selectors can choose the same CPU before either task is enqueued.
> >
> > Use reservoir sampling for equal exit latencies, resetting the candidate
> > count when a shallower candidate appears. Use the per-CPU scheduler PRNG
> > and reciprocal_scale() to avoid variable division or a second scan.
> >
> > Use a u64 latency key with U64_MAX for unpublished states. Published
> > states take precedence; when none are found, sample among the idle CPUs
> > without a published state.
> >
> > Signed-off-by: Christian Loehle <christian.loehle@arm.com>
>
> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Thanks, let me go queue this.
prev parent reply other threads:[~2026-09-18 11:43 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-17 15:39 [PATCH v2 0/2] sched/fair: Randomize equally shallow idle CPU picks Christian Loehle
2026-09-17 15:39 ` [PATCH v2 1/2] sched/fair: Drop idle recency from slow-path CPU selection Christian Loehle
2026-09-17 15:39 ` [PATCH v2 2/2] sched/fair: Randomize equally shallow slow-path candidates Christian Loehle
2026-09-17 16:06 ` Vincent Guittot
2026-09-18 11:43 ` Peter Zijlstra [this message]
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