From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=90.155.50.34 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793955212; b=QT0zHsbBkIfe9oz0TUXydkgCmLpQeGF5CI5Gr2V/DVACf1AcXy9vb9d/Yu/2ueQHWlRL qskDnDc6iS4RX6Iyvhs3Yik9QGJdTufYkNjTL57AAtPme+iLp0FudT8S45LmCrr5u9Znp sBCXACV+i2BWBN7Ijbz0MPSAv6n7Plfgaxxbg3VbDAj94gMNWuATsv43Wjz+Avo6H0lcZ yK3tp6Vg0EL7TxcNtYWEybiB5iT45gYrX/U/zrCznrtI8MgHxy3/3PJdsKVywVasEaLtZ VaaM56JtUBnLrwFekc7NA+5QDyHUOAYn13qbPCgZMpFHKwI9rX3wLp8HAAD5lFmq+PQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793955212; h=DMARC-Filter:DKIM-Signature:Received:Received:Date:From:To:Cc: Subject:Message-ID:References:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; bh=McsrHN1OLvADKIlnH9mAKDVt7MK1OnBq7IFPGjbrecM=; b=IWGw3FZdlvZSWuOaAYQ1xaJB5dRpSdcP5kbYNwuOvshmp75stAyH3arCzdtoqKZrxGvY Q8o7GhBrvX0pL0bdHsCuWKa/JcN/Y3Vy9DkRnMJDQq5dJJdyHfl0TlSxPRembcA8+JF3A oiCpi/kCu5AQPr0tsEby36C3p2+Oh0zv1rolp3eYm/92Sdk7vOdqVfyY2YzRO0tbCXoeQ PcD8bnbOZg2cfNcJCHPRLoQdf0ZcUYEBOoY8fwDuwUXVmdPu6KgUOQpjgI8jVL5l+KjXH dSlHYLJkDq25glqrAPiL807Kn/gnHiNLZYqh+6i3xQdNx7PMZWisc4fb6V5NI0aq5CQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=casper.20170209 header.b=h8fQ3Sgq; arc=none smtp.remote-ip=90.155.50.34 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 47F9B606A328 for ; Fri, 6 Nov 2026 08:53:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 47F9B606A328 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, unprotected) header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=casper.20170209 header.b=h8fQ3Sgq 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=McsrHN1OLvADKIlnH9mAKDVt7MK1OnBq7IFPGjbrecM=; b=h8fQ3SgqdurAZqrSrpnn4U+7v3 XTWWQxACJIOKJsD82+JTNVHh3oLg7ogpG8l8/70/TgefYe88R3RLRhdb2ixGpo9pZqdtwXfT1WjjN bIuJzv9W1941HVf3JUixXYxyuroEwgtZysLbUad61eNS3E+4+rn8pk48xxV/P2aiLbL87QxyBYt5P 3qCiUJ1rFy4/xRrj0IAx9pWCh09FdQEPva1IhcCx4qsE2BPfA8QCWmmpgQSgnLUbj4NrZWmJdErsh 8i8LfTztVL+JCMybRAtBIyl/WgYK64+WL/r3RNMSnh282DWGluEH34ZXe3OHG6R8oupXuvCCpBuCR wYG/fcSA==; 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 4.100.1 #2 (Red Hat Linux)) id 1xPFhK-00000002FyW-088u; Fri, 06 Nov 2026 08:53:22 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id E7313300302; Fri, 06 Nov 2026 09:53:20 +0100 (CET) Date: Fri, 6 Nov 2026 09:53:20 +0100 From: Peter Zijlstra To: Kayra Cizmeci Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, joshdon@google.com, tj@kernel.org, jakub@okonski.org Subject: Re: [PATCH 2/3] sched/fair: Make cfs_rq::idle the sum of ancestor tg::idle Message-ID: <20261106085320.GB1922751@noisy.programming.kicks-ass.net> References: <20261105165525.011876858@infradead.org> <20261105170157.616859418@infradead.org> <20261106083106.GC1779021@noisy.programming.kicks-ass.net> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261106083106.GC1779021@noisy.programming.kicks-ass.net> On Fri, Nov 06, 2026 at 09:31:06AM +0100, Peter Zijlstra wrote: > > > --- a/kernel/sched/fair.c > > > +++ b/kernel/sched/fair.c > > > @@ -15594,8 +15594,10 @@ static void set_next_task_fair(struct rq > > > hrtick_start_fair(rq, p); > > > } > > > > > > -void init_cfs_rq(struct cfs_rq *cfs_rq) > > > +void init_cfs_rq(struct cfs_rq *cfs_rq, struct cfs_rq *parent) > > > { > > > + if (parent) > > > + cfs_rq->idle = parent->idle; > > > > AFAICT this creates a race: > > > Or am I missing something? > > Nah, you're right, this needs rq->lock. Something like so.. --- --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -8970,7 +8970,7 @@ void __init sched_init(void) rq->nr_running = 0; rq->calc_load_active = 0; rq->calc_load_update = jiffies + LOAD_FREQ; - init_cfs_rq(&rq->cfs, NULL); + init_cfs_rq(&rq->cfs); init_rt_rq(&rq->rt); init_dl_rq(&rq->dl); #ifdef CONFIG_FAIR_GROUP_SCHED --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -15594,10 +15594,8 @@ static void set_next_task_fair(struct rq hrtick_start_fair(rq, p); } -void init_cfs_rq(struct cfs_rq *cfs_rq, struct cfs_rq *parent) +void init_cfs_rq(struct cfs_rq *cfs_rq) { - if (parent) - cfs_rq->idle = parent->idle; cfs_rq->tasks_timeline = RB_ROOT_CACHED; cfs_rq->zero_vruntime = (u64)(-(1LL << 20)); raw_spin_lock_init(&cfs_rq->removed.lock); @@ -15648,7 +15646,7 @@ int alloc_fair_sched_group(struct task_g goto err; se = tg_se(tg, i); - init_cfs_rq(cfs_rq, tg_cfs_rq(parent, i)); + init_cfs_rq(cfs_rq); init_tg_cfs_entry(tg, cfs_rq, se, i, tg_se(parent, i)); init_entity_runnable_average(se); } @@ -15661,19 +15659,20 @@ int alloc_fair_sched_group(struct task_g void online_fair_sched_group(struct task_group *tg) { - struct sched_entity *se; - struct rq_flags rf; - struct rq *rq; int i; for_each_possible_cpu(i) { - rq = cpu_rq(i); - se = tg_se(tg, i); - rq_lock_irq(rq, &rf); + struct cfs_rq *cfs_rq = tg_cfs_rq(tg, i); + struct sched_entity *se = tg_se(tg, i); + struct rq *rq = cpu_rq(i); + + guard(rq_lock_irq)(rq); + update_rq_clock(rq); attach_entity_cfs_rq(se); sync_throttle(tg, i); - rq_unlock_irq(rq, &rf); + + cfs_rq->idle = tg_cfs_rq(tg->parent, i)->idle; } }