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 32D9D3EA6C for ; Fri, 15 Dec 2023 15:15:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=none (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="o3P6fWjz" 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=zjfLxXDbrMtHt/IyeLuzZsV/+Apk943HO/rR5xaRTGI=; b=o3P6fWjzbD/C8zfyWzMpXV6vTA Gy9uSbGXW+ugPp30wKDTaFcGsu7humKRDLTD7YxPkju0ayrcMDYIAA3nanHL5zqbL2OJi4vOJvBic YZMdYh9S29R5THiAwWgZ21NOUDMLvr+bNn4NbxY72VWFLW5O/IjeHSkZzpNw4+Ig3EO62e69nk4Dc 2b6jvZygLQ2i6Q33TP6uTrfXbJApxg2HmEoFsuWM3d0DePXIOPMjkrwP+yuHUOmjJ1xhPjE3yMSF7 KUM/GYRRwP1qgz9pjOSY+2IdxuaOecvZ6f6y//vWHjQxrbvsqyGYLzYa9rzKSP0CiyE/SPDs8EYI8 wMrh9Fbw==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1rE9tc-009xM4-05; Fri, 15 Dec 2023 15:14:37 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id CF1243005B2; Fri, 15 Dec 2023 16:14:34 +0100 (CET) Date: Fri, 15 Dec 2023 16:14:34 +0100 From: Peter Zijlstra To: Keisuke Nishimura Cc: Ingo Molnar , Abel Wu , Josh Don , Mel Gorman , Xunlei Pang , Dietmar Eggemann , Valentin Schneider , Julia Lawall , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] sched/fair: take into account scheduling domain in select_idle_smt() Message-ID: <20231215151434.GK36716@noisy.programming.kicks-ass.net> References: <20231214175551.629945-1-keisuke.nishimura@inria.fr> 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: <20231214175551.629945-1-keisuke.nishimura@inria.fr> On Thu, Dec 14, 2023 at 06:55:50PM +0100, Keisuke Nishimura wrote: > When picking out a CPU on a task wakeup, select_idle_smt() has to take > into account the scheduling domain of @target. This is because cpusets > and isolcpus can remove CPUs from the domain to isolate them from other > SMT siblings. > > This fix checks if the candidate CPU is in the target scheduling domain. > > The commit df3cb4ea1fb6 ("sched/fair: Fix wrong cpu selecting from isolated > domain") originally proposed this fix by adding the check of the scheduling > domain in the loop. However, the commit 3e6efe87cd5cc ("sched/fair: Remove > redundant check in select_idle_smt()") accidentally removed the check. > This commit brings the check back with the tiny optimization of computing > the intersection of the task's CPU mask and the sched domain mask up front. > > Fixes: 3e6efe87cd5c ("sched/fair: Remove redundant check in select_idle_smt()") Simply reverting that patch is simpler no? That cpumask_and() is likely more expensive than anything else that function does. And I'm probably already in holiday more, but I don't immediately understand the problem, if you're doing cpusets, then the affinity in p->cpus_ptr should never cross your set, so how can it go wrong? Is this some isolcpus idiocy? (I so hate that option) > Signed-off-by: Keisuke Nishimura > Signed-off-by: Julia Lawall > --- > kernel/sched/fair.c | 15 +++++++++++---- > 1 file changed, 11 insertions(+), 4 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index bcd0f230e21f..71306b48cf68 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -7284,11 +7284,18 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu > /* > * Scan the local SMT mask for idle CPUs. > */ > -static int select_idle_smt(struct task_struct *p, int target) > +static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target) > { > int cpu; > + struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_rq_mask); > + > + /* > + * Check if a candidate cpu is in the LLC scheduling domain where target exists. > + * Due to isolcpus and cpusets, there is no guarantee that it holds. > + */ > + cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr); > > - for_each_cpu_and(cpu, cpu_smt_mask(target), p->cpus_ptr) { > + for_each_cpu_and(cpu, cpu_smt_mask(target), cpus) { > if (cpu == target) > continue; > if (available_idle_cpu(cpu) || sched_idle_cpu(cpu)) > @@ -7314,7 +7321,7 @@ static inline int select_idle_core(struct task_struct *p, int core, struct cpuma > return __select_idle_cpu(core, p); > } > > -static inline int select_idle_smt(struct task_struct *p, int target) > +static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target) > { > return -1; > } > @@ -7564,7 +7571,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target) > has_idle_core = test_idle_cores(target); > > if (!has_idle_core && cpus_share_cache(prev, target)) { > - i = select_idle_smt(p, prev); > + i = select_idle_smt(p, sd, prev); > if ((unsigned int)i < nr_cpumask_bits) > return i; > } > -- > 2.34.1 >