From: Peter Zijlstra <peterz@infradead.org>
To: Zhan Xusheng <zhanxusheng1024@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org,
Zhan Xusheng <zhanxusheng@xiaomi.com>
Subject: Re: [PATCH v4] sched/psi: Skip CPUs with zero non-idle delta in per-CPU aggregation
Date: Mon, 4 May 2026 10:04:34 +0200 [thread overview]
Message-ID: <20260504080434.GN3126523@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20260429100555.179348-1-zhanxusheng@xiaomi.com>
On Wed, Apr 29, 2026 at 06:05:55PM +0800, Zhan Xusheng wrote:
> collect_percpu_times() iterates over every possible CPU to build a
> non-idle-weighted average of the PSI state times. When a CPU has
> no PSI_NONIDLE delta for the current sampling interval:
> nonidle = nsecs_to_jiffies(times[PSI_NONIDLE]) = 0
> deltas[s] += times[s] * nonidle /* += 0 */
>
> so the weighted accumulation contributes nothing.
>
> get_recent_times() already sets the PSI_NONIDLE bit in
> cpu_changed_states iff the PSI_NONIDLE delta is non-zero. Use that
> bit to skip such CPUs early, as suggested by Johannes, avoiding the
> nsecs_to_jiffies() call.
>
> No functional change intended.
So presumably this is an optimization. Where is the data that justifies
this?
prev parent reply other threads:[~2026-05-04 8:04 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-03 10:00 [PATCH] sched/psi: Skip CPUs with zero non-idle jiffies in per-cpu aggregation Zhan Xusheng
2026-02-03 16:46 ` Johannes Weiner
2026-02-04 2:23 ` [PATCH v2] sched/psi: Skip CPUs with zero non-idle jiffies in per-CPU aggregation Zhan Xusheng
2026-03-13 3:48 ` [PATCH v3] " Zhan Xusheng
2026-04-29 10:05 ` [PATCH v4] sched/psi: Skip CPUs with zero non-idle delta " Zhan Xusheng
2026-05-04 8:04 ` Peter Zijlstra [this message]
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