From: Christian Loehle <christian.loehle@arm.com>
To: Vincent Guittot <vincent.guittot@linaro.org>,
Andrea Righi <arighi@nvidia.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
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>,
linux-kernel@vger.kernel.org,
Felix Abecassis <fabecassis@nvidia.com>
Subject: Re: [PATCH] sched/topology: Avoid spurious asymmetry from CPU capacity noise
Date: Tue, 24 Mar 2026 07:55:20 +0000 [thread overview]
Message-ID: <cbdb72fa-e9b1-45dd-a372-a5ced4966469@arm.com> (raw)
In-Reply-To: <CAKfTPtBYdwNGw1QHPABVgz5KX+rzWv=f1V8Kgde7CU1yX10g8A@mail.gmail.com>
On 3/24/26 07:39, Vincent Guittot wrote:
> On Tue, 24 Mar 2026 at 01:55, Andrea Righi <arighi@nvidia.com> wrote:
>>
>> On some platforms, the firmware may expose per-CPU performance
>> differences (e.g., via ACPI CPPC highest_perf) even when the system is
>> effectively symmetric. These small variations, typically due to silicon
>> binning, are reflected in arch_scale_cpu_capacity() and end up being
>> interpreted as real capacity asymmetry.
>>
>> As a result, the scheduler incorrectly enables SD_ASYM_CPUCAPACITY,
>> triggering asymmetry-specific behaviors, even though all CPUs have
>> comparable performance.
>>
>> Prevent this by treating CPU capacities within 20% of the maximum value
>
> 20% is a bit high, my snapdragon rb5 has a mid CPU with a capacity of
> 871 but we still want to keep them different
>
> Why would 5% not be enough?
I've also used 5%, or rather the existing capacity_greater() macro.
>[snip]
next prev parent reply other threads:[~2026-03-24 7:55 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-24 0:55 [PATCH] sched/topology: Avoid spurious asymmetry from CPU capacity noise Andrea Righi
2026-03-24 7:39 ` Vincent Guittot
2026-03-24 7:55 ` Christian Loehle [this message]
2026-03-24 8:08 ` Christian Loehle
2026-03-24 9:46 ` Andrea Righi
2026-03-24 10:29 ` Dietmar Eggemann
2026-03-24 11:01 ` Andrea Righi
2026-03-25 9:23 ` Dietmar Eggemann
2026-03-25 9:32 ` Andrea Righi
2026-03-25 11:16 ` Dietmar Eggemann
2026-03-25 12:25 ` Andrea Righi
2026-03-25 15:26 ` Dietmar Eggemann
2026-03-25 16:50 ` Andrea Righi
2026-03-25 12:48 ` Phil Auld
2026-03-24 9:39 ` Andrea Righi
2026-03-25 3:30 ` Koba Ko
2026-03-25 12:29 ` Andrea Righi
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