From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3E3644248B2 for ; Thu, 24 Sep 2026 10:05:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790244334; cv=none; b=HtsCKB6E5EId2tByRswBD7KtKisMzBZHZfHpdiobtSfChmKxI8UQmXjel/27UiFfKy0914lFpGyof6e8+4nyG28P4ygLJerLi0+jN+A2s446g7qaAmF0dsonxqE9x+kRxi/pISHr7SBGDTL3V8wRvwFNhUcFYLCFSK+pk7fBsjM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790244334; c=relaxed/simple; bh=YSeOZbycv01BwSJahdAB6QqLIHFMPt+kNhyjtCbM2qU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QafCE8WCQOA8pvcFVHIc+tqt0fwPvJnTr4eiCnn+QM2xMF5LEjsd9n5sVVgm5SJCWQiFU3QOGdHFyFe1TiDapmncehQpLXCrmM97l5bA4iBFD5tqrNWL8Q8waVkGCciGokOYm7JDPfSxnjFfFKFRGSJumVAF0lyej08+N9/uAQk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=GuAA0c+G; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="GuAA0c+G" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=pMlDbFY1DrOFbR3JyHn7RHNElhrPb+lBIPYkDBpaonE=; b=GuAA0c+GhXrInyDCg1NwZc36fo 4C03HtX7D9B+gkyuCDIYIXAih8o0RIwoiWhCJ1DOja1bL8iMaQ/M/T+4+2TFLZXYBCQjV4MWEd4dH PLZONK619i+ZZMdXqZ0Wppdbn0eMsGgPMO4aAvAx3u61dMWlJCnV0yxgsgce0sxGsFV0FE7kl3Eqa l90z6g/eliADm5K0mre3swQn3bdWA9SNDKTKDBGoC4NEwLbthqkgArARrYrmzRdMTUL1aC0QhyyY7 Sik6BLJ+E+Xi7X8UjHvSHRphwilL7VtuLsjEJ4a1LJEruWx2XAJZl0pjNKhST9ym5xpLIHekHFbrb DSxmK89A==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.99.2 #2 (Red Hat Linux)) id 1x9gKI-0000000FopH-0Yyj; Thu, 24 Sep 2026 10:05:14 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 432973008D6; Thu, 24 Sep 2026 12:05:13 +0200 (CEST) Date: Thu, 24 Sep 2026 12:05:13 +0200 From: Peter Zijlstra To: "Shubhang Kaushik (Ampere)" Cc: Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Christopher Lameter , Shubhang Kaushik , Madadi Vineeth Reddy , Shrikanth Hegde , linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] sched: Clarify WF_SYNC wakeup semantics Message-ID: <20260924100513.GE4121339@noisy.programming.kicks-ass.net> References: <20260922-sched-wf-sync-doc-v3-1-23ebe9e27bef@gentwo.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260922-sched-wf-sync-doc-v3-1-23ebe9e27bef@gentwo.org> On Tue, Sep 22, 2026 at 02:57:05PM -0700, Shubhang Kaushik (Ampere) wrote: > 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: Shubhang Kaushik (Ampere) > --- Thanks!