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 3B7E53B8958; Fri, 5 Jun 2026 15:13:11 +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=1780672392; cv=none; b=J2/ywGQwRBFsR6nlRPl8pmg/+6cndN+E2ZjdxIvisTbrEZrMU4TCpCg4a2OMMjbXej7mqPlHZpWgdHV2NSZwhYMFu54avj11FUVYuN44AtWbnrGwfoWVEHodVxOZurtCAkPDAqGDjAkscn7Ig42UYu0tOQWjPBHWy+vrN5rLj+k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780672392; c=relaxed/simple; bh=SZXTFqBeWNU8o2baX8AIUXgoUdkdWZrTkypA0qEaBvY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=HNHP3o+OTaZNch8JpPo/gg4lgQWztRmnNbPtmTYwF/DXYcFS6r6BS47NnyyIhLtp//4CdUliIKHZz8z3wurhTZD3VHzh6bQayyb6zdLbmNQ1S89LrD6itnoCSw0J+jS4ybzh8PgWXv+za4vwdUD9Oef1gZyl6gVxrGVY16jg33I= 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=OrV5u+9F; 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="OrV5u+9F" 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=rplKE1cDt2PxD7RNYFurKRhUkQYpl++hHWZ6g039jnI=; b=OrV5u+9FOmIuDrXfEmU8JYwOGj GFoqvr2ddOeTPi7mhwD4KZtxyJGhHRTLHx6uR8j7YCoPUAOclo4EzrmU6M51dWgPCRnl0EbyE3448 I67S94JQoS1S8Zf200tNI/RC46tcFTm5LPKZTGhv1lGhLZW0M57qFqK06J9yWvmKLBw0m0OvWBLdq 3i9rOyeSb9peIkF+KrFnH4FJVlThqdErW+pBjN5QWGCjQZVgx7ncl6DbqoylKv2iaDcY0ltAxhUZK ZG0GqtgLaFIFCW4YOtzjnrEGdFDt69vSmqIpSKcmIRg0MP2kJpxzHriZKc31ltn5RAGd9O50ky3kM s93ulp8Q==; Received: from 2001-1c00-8d85-4b00-266e-96ff-fe07-7dcc.cable.dynamic.v6.ziggo.nl ([2001:1c00:8d85:4b00:266e:96ff:fe07:7dcc] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.99.2 #2 (Red Hat Linux)) id 1wVW9M-0000000FkOk-0E82; Fri, 05 Jun 2026 15:07:56 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 0B4153001FD; Fri, 05 Jun 2026 17:07:54 +0200 (CEST) Date: Fri, 5 Jun 2026 17:07:53 +0200 From: Peter Zijlstra To: mingo@kernel.org Cc: longman@redhat.com, chenridong@huaweicloud.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, 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 v3 2/7] sched/fair: Add cgroup_mode: up Message-ID: <20260605150753.GA3117850@noisy.programming.kicks-ass.net> References: <20260605105513.354837583@infradead.org> <20260605124051.450303977@infradead.org> Precedence: bulk X-Mailing-List: cgroups@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: <20260605124051.450303977@infradead.org> On Fri, Jun 05, 2026 at 02:40:15PM +0200, Peter Zijlstra wrote: > Instead of calculating the proportional fraction of the group weight for each > CPU, just give each CPU the full measure, ignoring these pesky SMP problems. > > This makes the SMP cgroup fraction (F_g_n) equal to 1, and ensures a single > task in a cgroup competes on equal footing to a task in a level above. > > However, as already explored, this is not a very good policy because it gets > the SMP weight distribution wrong. Included for completeness. > > Signed-off-by: Peter Zijlstra (Intel) > --- > kernel/sched/debug.c | 5 ++++- > kernel/sched/fair.c | 31 +++++++++++++++++++++++++++++-- > kernel/sched/sched.h | 1 + > 3 files changed, 34 insertions(+), 3 deletions(-) > > --- a/kernel/sched/debug.c > +++ b/kernel/sched/debug.c > @@ -271,6 +271,7 @@ static ssize_t sched_dynamic_write(struc > if (mode < 0) > return mode; > > + __sched_cgroup_mode_update(mode); > sched_dynamic_update(mode); > > *ppos += cnt; Yeez, I'm not sute WTF happened here. Let me go fix that up.