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Date: Fri, 25 Sep 2026 20:35:36 +0200
From: Ingo Molnar <mingo@kernel.org>
To: linux-kernel@vger.kernel.org
Cc: linux-tip-commits@vger.kernel.org,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>, x86@kernel.org
Subject: Re: [tip: sched/core] sched: Clarify WF_SYNC wakeup semantics
Message-ID: <ara--PcvTbdm1zbs@gmail.com>
References: <20260922-sched-wf-sync-doc-v3-1-23ebe9e27bef@gentwo.org>
 <179033364193.2819794.10008973300214008226.tip-bot2@tip-bot2>
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* tip-bot2 for Shubhang Kaushik (Ampere) <tip-bot2@linutronix.de> wrote:

> The following commit has been merged into the sched/core branch of tip:
> 
> Commit-ID:     e4c353c3933968fe8efecb269fdbe3baa1d1ddd0
> Gitweb:        https://git.kernel.org/tip/e4c353c3933968fe8efecb269fdbe3baa1d1ddd0
> Author:        Shubhang Kaushik (Ampere) <sh@gentwo.org>
> AuthorDate:    Tue, 22 Sep 2026 14:57:05 -07:00
> Committer:     Peter Zijlstra <peterz@infradead.org>
> CommitterDate: Fri, 25 Sep 2026 12:45:59 +02:00
> 
> sched: Clarify WF_SYNC wakeup semantics
> 
> The synchronous waitqueue wakeup comments currently state that a
> synchronous wakee will not be migrated to another CPU. This is not
> guaranteed by the scheduler wakeup path.
> 
> WF_SYNC is an advisory hint that the caller expects the waker to
> schedule away soon. Scheduler classes may use it for placement or
> preemption, but callers must not rely on it to prevent migration,
> preserve CPU locality, or make the wakee run next.
> 
> Keep this contract next to the flag definition, remove the stale
> waitqueue wording, and make the locked helper refer to the unlocked
> variant.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Link: https://patch.msgid.link/20260922-sched-wf-sync-doc-v3-1-23ebe9e27bef@gentwo.org

JFYI, I've added Shubhang's SOB which is missing from the commit:

    Signed-off-by: Shubhang Kaushik (Ampere) <sh@gentwo.org>

Which I suppose got lost in some patch application mishap,
because it's present in the original.

Thanks,

	Ingo