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 A9454407582; Wed, 13 May 2026 12:43:36 +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=1778676220; cv=none; b=rUutRpvE4+UCBMEw7akusKUR0/iskxr+NQOjlyowvSRtkaIShFDXF6U5wMGaaiYwfDaYhX56J8O4PJGe9mXuXhKSaWI/D4csqGQLu1Tp6ll6927JIkBAQsdcgz6cTdhTzGe8FrEgTunrQUuFP3YzxwqFCY7OqC/2aiKrusi9iwE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778676220; c=relaxed/simple; bh=gRPvs6PXPbu7knhieTEtFOxn5jJTFgZyfo5qVpi9dGI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=dGdr0TZDwaCL1+q1z0RQKZa38qbjNLXd5ZD5YJbxrP9aqvglGt2ZlMY3vg52kod8DENZOYLYqJ7Tu1p7wLIvZaGu/MwY3F2ugXutSETu9NKR08DyyevExj5/FKk5xdmxxBQVapZRFfOfO6rzy5CY4mvdtwN9HkVREFYJWiJ9BvI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=ee2tYia9; 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=none 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="ee2tYia9" 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=Y3vovCO+Igd7oq8tTCnKK+WLaG5HU8hllZSY20e2fe0=; b=ee2tYia9sDjXgybttdycQlDgxX JkBbvZqisnf/ZI7K2RT4gzxKzlvLfZVcO6rzLsooXHpx3TWII1ysmq3r6fjXoO7EdNeJ1CXgL3IjI nL1SC3v4vuLTLHN3Arm0lpg0gY0mJ1unMxnVW/X9T4Hqu0LXopdCsEp5j9lhISBvB2CyT9G6kN8FW YjwtZqCOJZAa4+cBw6nwHWJP61GU85MLDT/Rzgip+z95n6vMIruPIN/8u36LLjQXAMBwedT/D+5bo bdrF/wJ9bs+AM3yPvnFHRpT+aDkZSCitP74dhXGVEaCSKmRAhs1GNyc2PdmtS1/VLQm11+1YQwZDF 8m0B+XKQ==; 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 4.99.1 #2 (Red Hat Linux)) id 1wN8vd-0000000HS4U-1Vvc; Wed, 13 May 2026 12:43:09 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 82C5F300382; Wed, 13 May 2026 14:43:08 +0200 (CEST) Date: Wed, 13 May 2026 14:43:08 +0200 From: Peter Zijlstra To: Vincent Guittot Cc: mingo@kernel.org, longman@redhat.com, chenridong@huaweicloud.com, juri.lelli@redhat.com, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, tj@kernel.org, hannes@cmpxchg.org, mkoutny@suse.com, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, jstultz@google.com, kprateek.nayak@amd.com, qyousef@layalina.io Subject: Re: [PATCH v2 00/10] sched: Flatten the pick Message-ID: <20260513124308.GA1283187@noisy.programming.kicks-ass.net> References: <20260511113104.563854162@infradead.org> <20260513113510.GK1889694@noisy.programming.kicks-ass.net> 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: <20260513113510.GK1889694@noisy.programming.kicks-ass.net> On Wed, May 13, 2026 at 01:35:10PM +0200, Peter Zijlstra wrote: > On Tue, May 12, 2026 at 10:42:33AM +0200, Vincent Guittot wrote: > > > I haven't reviewed the patches yet but I ran some tests with it while > > testing sched latency related changes for short slice wakeup > > preemption. I have some large hackbench regressions with this series > > on HMP system with and without EAS. those figures are unexpected > > because the benchs run on root cfs > > > > One example with hackbench 8 groups thread pipe > > tip/sched/core tip/sched/core +this patchset +this patchset > > slice 2.8ms 16ms 2.8ms 16ms > > dragonboard rb5 with EAS > > 0,748(+/-4,6%) 0,621(+/-3.6%) +17% 1,915(+/-7.9%) -156% > > 0,689(+/- 9.1%) +8% > > > > radxa orion6 HMP without EAS > > 0,588(+/-5.8%) 0,677(+/-5.9%) -15% 1,505(+/-10%) -156% > > 1,071(+/-5.9%) -82% > > > > Increasing the slice partly removes regressions but tis is surprising > > because the bench runs at root cfs and I thought that results will not > > change in such a case > > D'oh :/ > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index e54da4c6c945..77d0e1937f2c 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -9071,7 +9071,7 @@ static void wakeup_preempt_fair(struct rq *rq, struct task_struct *p, int wake_f > enum preempt_wakeup_action preempt_action = PREEMPT_WAKEUP_PICK; > struct task_struct *donor = rq->donor; > struct sched_entity *nse, *se = &donor->se, *pse = &p->se; > - struct cfs_rq *cfs_rq = task_cfs_rq(donor); > + struct cfs_rq *cfs_rq = &rq->cfs; > int cse_is_idle, pse_is_idle; > > /* With that fixed, I now get: vanilla slice(*) FPS min 3.0 11.1 avg 44.7 57.3 max 88.1 96.2 FT min 9.1 8.0 avg 41.4 21.0 max 157.2 53.9 FPS (Frames Per Second) FT (FrameTime) Which I suppose shows we now preempt less. Its still significantly better with reduced slice, but not as good as it was.