From: Peter Zijlstra <peterz@infradead.org>
To: Srikar Dronamraju <srikar@linux.ibm.com>
Cc: linux-kernel@vger.kernel.org,
Michael Ellerman <mpe@ellerman.id.au>,
Madhavan Srinivasan <maddy@linux.ibm.com>,
linuxppc-dev@lists.ozlabs.org, Ben Segall <bsegall@google.com>,
Christophe Leroy <christophe.leroy@csgroup.eu>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>, Mel Gorman <mgorman@suse.de>,
Nicholas Piggin <npiggin@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
Valentin Schneider <vschneid@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>
Subject: Re: [PATCH 1/2] sched: Feature to decide if steal should update CPU capacity
Date: Tue, 28 Oct 2025 12:18:13 +0100 [thread overview]
Message-ID: <20251028111813.GK3245006@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20251028104255.1892485-1-srikar@linux.ibm.com>
On Tue, Oct 28, 2025 at 04:12:54PM +0530, Srikar Dronamraju wrote:
> At present, scheduler scales CPU capacity for fair tasks based on time
> spent on irq and steal time. If a CPU sees irq or steal time, its
> capacity for fair tasks decreases causing tasks to migrate to other CPU
> that are not affected by irq and steal time. All of this is gated by
> NONTASK_CAPACITY.
>
> In virtualized setups, a CPU that reports steal time (time taken by the
> hypervisor) can cause tasks to migrate unnecessarily to sibling CPUs that
> appear to be less busy, only for the situation to reverse shortly.
>
> To mitigate this ping-pong behaviour, this change introduces a new
> scheduler feature flag: ACCT_STEAL which will control whether steal time
> contributes to non-task capacity adjustments (used for fair scheduling).
Please don't use sched_feat like this. If this is something that wants
to be set by architectures move it to a normal static_branch (like eg.
sched_energy_present, sched_asymc_cpucapacity, sched_cluster_active,
sched_smt_present, sched_numa_balancing etc.).
next prev parent reply other threads:[~2025-10-28 11:18 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-28 10:42 [PATCH 1/2] sched: Feature to decide if steal should update CPU capacity Srikar Dronamraju
2025-10-28 10:42 ` [PATCH 2/2] powerpc/smp: Disable ACCT_STEAL for shared LPARs Srikar Dronamraju
2025-10-28 11:18 ` Peter Zijlstra [this message]
2025-10-28 11:42 ` [PATCH 1/2] sched: Feature to decide if steal should update CPU capacity Srikar Dronamraju
2025-10-28 15:05 ` Shrikanth Hegde
2025-10-29 6:08 ` K Prateek Nayak
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