From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 D69DE1A6809 for ; Tue, 7 Apr 2026 13:45:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775569536; cv=none; b=siTwsWyVGbEoUgKEWXnYQM5dAAma8Dhs79XnsYQE9oamUUJNbuGvDFtkvtQ9JXApLN8O2ogNcnSBKIqoIz1wO78bj7LaBiEYTJyxPSWbBluzt/N2kvkZLg/flpzqlZjFMDprEWJ0VFZi/DCD9wHDlz9JtX+ZVm+tyujmGF+ZFIo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775569536; c=relaxed/simple; bh=WWsvR4yquasPEW/Z4H9DxxbnJD5OWixsttUsz7jSM14=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=tg0fCBQAnjD32xa3N/K+64GdKlNssp+n49kuFhEtO25Cj3kdYR+YH0Dhhu56ERqZKu9HRGdbMT0AQWYIzBIZel9wxpMVLvHkjHJ9O7cBvGv6zu9iYHLvkZq4c3L/BC4Z99jj1638dybopZ8GnqqM287q6Vj5cFO2SZ2bf20h3W8= 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=ZAcQ0jma; arc=none smtp.client-ip=90.155.50.34 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="ZAcQ0jma" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; 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=ivADiZcdZdf25P7ZCE49GVcfVA4b+mKuijFj+pieM0E=; b=ZAcQ0jmasTgCkrZSwClkzro5YD BW7WFnzjMl97vakiI4WUfN71BHV6l+axvxFlEP2Px5w3Wywg4MWt2ApL46dK4djoq9UlkQQr1hFz4 PqzwzPGXVWY3fFs8JH7C5qbmv2TM7LwXZGxGgDvgxZy0yuhQJsv1qqq/HSRAr1nWYrCbwVONnAzZF R6jlYjjiOpexAAKwjwQkXS2nZQ+WNLxs869hFiuVrq2Ff750NAAWG3b2sD9LtD38phEow/1csoqL0 mqPbkVbnJzdUMGQlBclELWpb1hbFymEPNjyZR1jkhvTpvf2jYd7OKOjBhmgF+i0Hxj8FzKzQNG1Wk ymo3fSsQ==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1wA6k4-00000003gnI-1uJb; Tue, 07 Apr 2026 13:45:20 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 4151C3005E5; Tue, 07 Apr 2026 15:45:19 +0200 (CEST) Date: Tue, 7 Apr 2026 15:45:19 +0200 From: Peter Zijlstra To: William Montaz Cc: vincent.guittot@linaro.org, bsegall@google.com, dietmar.eggemann@arm.com, dsmythies@telus.net, juri.lelli@redhat.com, kprateek.nayak@amd.com, linux-kernel@vger.kernel.org, mgorman@suse.de, mingo@kernel.org, quzicheng@huawei.com, rostedt@goodmis.org, shubhang@os.amperecomputing.com, vschneid@redhat.com, wangtao554@huawei.com, Greg Kroah-Hartman Subject: Re: [PATCH v2 6/7] sched/fair: Revert 6d71a9c61604 ("sched/fair: Fix EEVDF entity placement bug causing scheduling lag") Message-ID: <20260407134519.GH3738010@noisy.programming.kicks-ass.net> References: <20260324100126.3502-1-willymontaz@gmail.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 Content-Disposition: inline In-Reply-To: <20260324100126.3502-1-willymontaz@gmail.com> On Tue, Mar 24, 2026 at 10:01:26AM +0000, William Montaz wrote: > Hi, > > > Zicheng Qu reported that, because avg_vruntime() always includes > > cfs_rq->curr, when ->on_rq, place_entity() doesn't work right. > > > Specifically, the lag scaling in place_entity() relies on > > avg_vruntime() being the state *before* placement of the new entity. > > However in this case avg_vruntime() will actually already include the > > entity, which breaks things. > > This has proven to be harmful on our production cluster using kernel version 6.18.19 > I tested the following versions: > * LTS 5.10.252, 5.15.202, 6.1.166, 6.6.129, 6.12.77 --> no issue > * LTS 6.18.19 has the issue > * Stable 6.19.9 has the issue > * Mainline 7.0-rc5 has the issue > * Tip 7.0.0-rc5+ no issue > > Finally, I applied the patch to 6.18.19 LTS which solves the issue. However, we do not benefit from previous patches > such as [PATCH v2 5/7] sched/fair: Increase weight bits for avg_vruntime. > > Thus I would prefer to let you decide how you want to adress backport on 6.18 > > If you want I can share my patch file, let me know. I've (finally!) had a look at stable-6.18.y and yes, I think this can be backported without too much issue. Feel free to submit a backport to stable for this.