From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr2-f12.google.com (mail-wr2-f12.google.com [74.125.225.76]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B6FD1471408 for ; Sun, 4 Oct 2026 17:30:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.225.76 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791135040; cv=none; b=rwEjxUGGXI6Ev5IRLKO0qYgkvHOH9Cd73xLGhNecXrgs4e2TFof0cCyiyPZJjsaYN8Z+HCRxZEv0fSPrWVP1Cg3dbEr1imilCjlgDlpm8TssHq3/m1ncMddtZD41CTRXwrg6VyiS5YxR+zhs4vggUUkLo0ewIgb2UgIAgABEB8A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791135040; c=relaxed/simple; bh=WXL5LZkJrtzk9YPJU9X6JrPpHjTvu4EMRFegf6wNEUM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=XxHDfu0oxfwtu8EnK13b9Ww3B5C5+8lo5zDDeXW9opar7qpMsax+RFou/MFCUd/i9KxH5lCFxsCwRQpOxwGl5r4zdGpXxkMm5TXtNgBMefF+S4AIgrGadyLILnzA1BfIWubmH575aaznc+dJ5Y4uxaXx6NzI5XUopQzeKIGcJQc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=GZlhxpcP; arc=none smtp.client-ip=74.125.225.76 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="GZlhxpcP" Received: by mail-wr2-f12.google.com with SMTP id ffacd0b85a97d-482e1b55da8so97689f8f.0 for ; Sun, 04 Oct 2026 10:30:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1791135037; x=1791739837; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to:content-type; bh=K9BNRj1cE9nvNKn/WOlSUCpAG1T6oqBgGlxlrkhv5sI=; b=GZlhxpcPYBjSozAyWHbMWJlJts7e0Xi/f6rNEHP1OecszGrF8bS7Qc8AC3Hzt+w6ql yTUwxTd/G7ovu8Cs5RzmWcsGM0jnUAVc4Xz8VeIEvAM3zd7kZphqg9oF0jycGN+sCnQe UbDS+LsEllLf2+0BQH0+PFE/uCxK7INUPCtdiZ9IBkvUm8TsTjer8FJevLlBROHM9LDE sP94p+LYUpje2FyX8QnYpF0HqyD0AALNYqTtBlIM+XuoHk3KwpYjZBF5vb4znY3KatIi afAF0d8ElNPywuZ25iTjddvJ+DPVBz/4YQz1soSCER0D2AxjXgjOokX5P5HJWApzxb67 +oHg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1791135037; x=1791739837; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to:content-type; bh=K9BNRj1cE9nvNKn/WOlSUCpAG1T6oqBgGlxlrkhv5sI=; b=nly73rrrr9awRhI1j/WvPSB0St624EKIHugg2qfeB7oCPVQIx88QIbz/1JWeyOsq1g uyOlOjm5/ejiRajrQGJaKrPw8W+17FWayA8qSoEQcol9sEwgtFV3EhRcmm/M/CMfAMwx jyHgfljowinYQQqgbMFUCh5/CoNBcskPgewAFIKdEgOonu3VGR9k7wXIpft39zEj6p8+ XJr7JKevxvS8H2fg7v2xLzv9jywFIMQh1Y/0qXnogCoE9lHAauFcSz6YqWlzAwChi5vW 7yZQpN2E2QfVzxDuz11HVlV1bIqb3H8lbPIB8s+raldfWsT4R+7l5GcdhmTPGlEeQAuk Z/tw== X-Forwarded-Encrypted: i=1; AKwUvBw7+yk3vbHXXPXYBhhmMbhKrCSL0tBls8xJe6Q4OaGAhLLYAC3/SU1QTwFjgWyGDAID8Moz6+lyo7Gt4nI=@vger.kernel.org X-Gm-Message-State: AFq9FYKu+8zm5ECFEQnlAG6gFV3KB7k2LrkVz1CVbw+0sZsKHo6aXnX/ pabYFjSXdUxg+mj9ygjj9psIZgrC1I5dTGQmgoqWUuKqI6Em2N/dXl1J X-Gm-Gg: AYBFou2tAsZOoXJmVo86WWGELX11WWnFIxJH4XEDAkzUsQuedST+KdsgQg4fDybBTk/ mS65Ip7pgGiGztDlGFLvjZ62TVtPC47I6l1kGWBzmdhytip/Niu1o8dzOrOrnFya28nCzn/4ksh mh7/5FZbPjhh/0EH6N77L7U0+YwCH3GthepTd5iXkONKJiqRNMTJcP94+txf+ES0dyD1xTsaIfK DlLyFx00SYexJ83sd9itvzRIcBNcIGDAWL9zZKhwdWbVH+mGafqhFxVPa2aNP5T6cMsT9kkJCnl gYu58aNOhbMX4Sj8F7nN4UacgAjzwN8FlOjECKIVYKWtArzI7hdxAnLWEeupUqxHsJ7xU6bnFvG NU2XEbawsU5Ivc7MEnclM7GS9+bhktNhUge2X6awJzzi4vPGHyXuoxx4vMgdi1UVG9osUPAivME wiVRyZaaQTpkHJeNQ+lMc7BcqrNkviK+JEjpKnlewBp53oJuKAtJNoYO56zjKzRDIVVDfELABOw 2sRA6zoPHXvaoM1nR9y/bLd32aKYzo= X-Received: by 2002:a05:6000:2f8a:b0:48c:4802:e253 with SMTP id ffacd0b85a97d-48c4802e368mr8983746f8f.6.1791135036570; Sun, 04 Oct 2026 10:30:36 -0700 (PDT) Received: from lima-kdev.local ([85.100.66.184]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48b382f8ab4sm18299306f8f.35.2026.10.04.10.30.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 04 Oct 2026 10:30:36 -0700 (PDT) From: Kayra Cizmeci To: vincent.guittot@linaro.org Cc: arighi@nvidia.com, bsegall@google.com, changwoo@igalia.com, christian.loehle@arm.com, dietmar.eggemann@arm.com, juri.lelli@redhat.com, kprateek.nayak@amd.com, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, lukasz.luba@arm.com, mgorman@suse.de, mingo@redhat.com, peterz@infradead.org, pierre.gondois@arm.com, qyousef@layalina.io, rafael@kernel.org, rostedt@goodmis.org, sched-ext@lists.linux.dev, sshegde@linux.ibm.com, tj@kernel.org, void@manifault.com, vschneid@redhat.com Subject: Re: [PATCH 02/18] sched/eevdf: Reset lag when waking up on idle cpu Date: Sun, 4 Oct 2026 20:30:32 +0300 Message-ID: <20261004173032.18867-1-kayracizmeci@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261002154415.2270586-3-vincent.guittot@linaro.org> References: <20261002154415.2270586-3-vincent.guittot@linaro.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit > When several tasks wake up simultaneously on an idle CPU, their final vlag > will depend of the ordering as the first one will lose its lag but not > the next ones. > Reset the lag when the enqueue happens while no fair task has already been > picked et set as the running task. There is a typo. ('et', also 'depend' and 'loose' Not sure that's all :>) > As a typical example: > CPU0 is idle > TA with vlag 0ms and TB with vlag 5ms wake up on CPU0 simultaneously. > Depending which grab the lock 1st the behavior will be different: > If TA is enqueued 1st, TB will be enqueued with a positive lag and will > be picked 1st. > But if TB is enqueued 1st, it will loose its positive vlag and both TA and > TB will have 0 vlag when fair will pick a task. > diff --git a/include/linux/sched.h b/include/linux/sched.h > index d7cc77181ef9..32d7077ef148 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -592,6 +592,7 @@ struct sched_entity { > u64 vruntime; > /* Approximated virtual lag: */ > s64 vlag; > + u32 vlag_seq; > /* 'Protected' deadline, to give out minimum quantums: */ > u64 vprot; > u64 slice; > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 8cda1d39b037..4c8f12fc8869 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -893,6 +893,7 @@ bool update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se) > vlag = min(vlag, 0); > } > se->vlag = vlag; > + se->vlag_seq = cfs_rq->idle_seq; > > return avruntime - vlag != se->vruntime; > } > @@ -914,9 +915,22 @@ void decay_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) > > rq = rq_of(cfs_rq); > > + /* You can't claim any lag when waking on idle CPU */ > + if (rq->curr == rq->idle) { > + se->vlag = 0; > + return; > + } > + > + /* Accessing remote rq task clock is a cost */ > if (flags & ENQUEUE_MIGRATED) > return; > > + /* CPU has been idle in between so the lag has been removed */ > + if (se->vlag_seq != cfs_rq->idle_seq) { > + se->vlag = 0; > + return; > + } > + > /* Compute sleep time */ > delta_exec = rq_clock_task(rq) - se->exec_start; > if (unlikely(delta_exec <= 0)) > @@ -8190,6 +8204,9 @@ static bool __dequeue_task(struct rq *rq, struct task_struct *p, int flags) > > dequeue_hierarchy(p, flags); > > + if (!cfs_rq->h_nr_queued) > + cfs_rq->idle_seq++; Shouldn't this skip DEQUEUE_SAVE? > + > if (sched_feat(PLACE_REL_DEADLINE) && !task_sleep) { > se->deadline -= se->vruntime; > se->rel_deadline = 1; > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index b98084e1f5b0..69a2a749e188 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -689,6 +689,7 @@ struct cfs_rq { > u64 sum_weight; > u64 zero_vruntime; > unsigned int sum_shift; > + u32 idle_seq; > > #ifdef CONFIG_SCHED_CORE > unsigned int forceidle_seq; Yeah, well AFAICT other things seems OK. Also, while trying to get this patch series on my tip branch I had a hard time. I was at the caves of git and b4 figthing with... Everything. Like there were no v2 tags on some of the patches so b4 didn't tracked them. I had to do some things by hand and finally it worked. (Not too greatly tho.) But who cares? :>. Thanks, Kayra