From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from gentwo.org (gentwo.org [62.72.0.81]) (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 8D4163C8724 for ; Fri, 24 Jul 2026 16:17:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=62.72.0.81 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784909838; cv=none; b=tfg3TXb/6aoDq3Kx5wjFyARKhgsrlkd35h8EkO6Y3ZxsiwdgSVeCOl5HcIQcMNKOReuKrLE/sN9tethqKwMVfppwo8fbnDIPLiTubUzIb6ywhTAZje647u7hbYC1fNLZLMJB8eRFx1gkvAIbEcIhmMBCg7Q1gjO+QWIlqW5ltD8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784909838; c=relaxed/simple; bh=cK/cmwEVpwYK1FMC0xYwJmbX1H1vnxhR1qr3rDUG/ik=; h=Date:From:To:cc:Subject:In-Reply-To:Message-ID:References: MIME-Version:Content-Type; b=Mb7kbcO6zg/XyVfcK9DJEhlp2Av5RcgSLjBZULG/eg7QJOXfwyOBLa8oUgnTURqgcxc7+4zSUtavKGi5oR5nPonbs/p4njfFo7Yp+yrJRvFV+YYpw4TRRkufSbqFF6wpCVKJ2oVxBqhgA6GCIpXku5o80NA0UyHMj4jHjd6iULY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=gentwo.org; spf=pass smtp.mailfrom=gentwo.org; dkim=pass (1024-bit key) header.d=gentwo.org header.i=@gentwo.org header.b=IMAW0z61; arc=none smtp.client-ip=62.72.0.81 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=gentwo.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gentwo.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=gentwo.org header.i=@gentwo.org header.b="IMAW0z61" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gentwo.org; s=default; t=1784909319; bh=cK/cmwEVpwYK1FMC0xYwJmbX1H1vnxhR1qr3rDUG/ik=; h=Date:From:To:cc:Subject:In-Reply-To:References:From; b=IMAW0z61bTVrx36OkV+nlwH1LRBZje+H8z6OZ/5slFCXruQ9RVyRX0JKArAdGMShc YXFDbpyyWJO5fnFIbOBAIFQMVV1CRG9PViOO3pGfDVYIrpzfZ4OhLJXiwj/Fb45++7 qcDjoslHB5kvq3DvzdlpEWC6WtzLhtfW+/8dPR1s= Received: by gentwo.org (Postfix, from userid 1007) id CE4D740B35; Fri, 24 Jul 2026 09:08:39 -0700 (PDT) Received: from localhost (localhost [127.0.0.1]) by gentwo.org (Postfix) with ESMTP id CC4E3408AE; Fri, 24 Jul 2026 09:08:39 -0700 (PDT) Date: Fri, 24 Jul 2026 09:08:39 -0700 (PDT) From: Shubhang To: Madadi Vineeth Reddy cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , "Christoph Lameter (Ampere)" , Shubhang Kaushik , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] sched/fair: Prefer waker CPU for reciprocal sync wakeups In-Reply-To: <60a584c5-25ac-4077-a725-a2f9ee74318d@linux.ibm.com> Message-ID: <519ca485-e2b5-a258-e1e4-b45c7feed57f@gentwo.org> References: <20260722-b4-sched-sync-wakeup-v2-1-f1164560b24b@gentwo.org> <60a584c5-25ac-4077-a725-a2f9ee74318d@linux.ibm.com> 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; format=flowed Hi Vineeth, On Fri, 24 Jul 2026, Madadi Vineeth Reddy wrote: > On 23/07/26 04:20, Shubhang Kaushik (Ampere) wrote: >> + READ_ONCE(p->last_wakee) == current && >> + prefer_sync_pair_cpu(p, cpu)) >> + return cpu; > > > The difference is SMT. POWER10/11 are SMT8: stacking there puts the pair on one thread while up to > seven siblings on the same core sit idle, sharing the same LLC. > > So instead of returning the waker's CPU, I'm looking at letting the waker's *core* count as idle > when the waker's runqueue has a single runnable task, so the wakee lands on a sibling thread. Thanks for the review, the distinction makes sense. In the case of non-SMT, the benefit I am seeing comes from stopping SIS from moving the reciprocal WF_SYNC wakee away from the wake-affine target. For v3, my plan is to keep this scoped to that non-SMT case under the existing SD_WAKE_AFFINE path and fold in Prateek's suggested cleanups. Would still wait for Christian/Prateek's SMT numbers to make sure this does not need additional SMT handling in this series. Regards, Shubhang Kaushik