From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D5693EB64DC for ; Tue, 11 Jul 2023 10:19:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230119AbjGKKTJ (ORCPT ); Tue, 11 Jul 2023 06:19:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51842 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230125AbjGKKS7 (ORCPT ); Tue, 11 Jul 2023 06:18:59 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 835DCDB for ; Tue, 11 Jul 2023 03:18:58 -0700 (PDT) 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=vtPd+yN1U4IqTK91Y6Crv4zudJrwwIEUOH8XFLUTBIk=; b=hvSnWQcO6AvhXvooZhbMvXWvsD nvp9B+MHb11v440DDTeYLHOU6tgz3037srEf9cWGxMnaFWPe9iyvnR31Effg9zOFfvg67JpHoTNP7 uLPgMxOwvbZYz7I4lEU4XTz+luagGQ12v5RAfAyCwtV63IwOgoGikK9mXfc6iPPmrTO9M7XnxLjeF yX+7V7VnIxskknxlXCXy1khl0hD8VLsPyAzEYaV2aExTAIaj/cabdW/dYVcEw1w76bpTGLde5t4JS tBYRP5PG94qiRTdOfuKEu8BitWE8Y/1ubwZvBm7t1CZh7gmxqd6qeiXQmWbt9WGXpv6mr+0UncX2H 1nL7eIhg==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1qJAS1-00FcUY-SJ; Tue, 11 Jul 2023 10:18:34 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 71A1E3002B1; Tue, 11 Jul 2023 12:18:32 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 587DB243429D0; Tue, 11 Jul 2023 12:18:32 +0200 (CEST) Date: Tue, 11 Jul 2023 12:18:32 +0200 From: Peter Zijlstra To: David Vernet Cc: linux-kernel@vger.kernel.org, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, gautham.shenoy@amd.com, kprateek.nayak@amd.com, aaron.lu@intel.com, clm@meta.com, tj@kernel.org, roman.gushchin@linux.dev, kernel-team@meta.com Subject: Re: [PATCH v2 5/7] sched: Implement shared runqueue in CFS Message-ID: <20230711101832.GF3062772@hirez.programming.kicks-ass.net> References: <20230710200342.358255-1-void@manifault.com> <20230710200342.358255-6-void@manifault.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230710200342.358255-6-void@manifault.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 10, 2023 at 03:03:40PM -0500, David Vernet wrote: > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 1451f5aa82ac..3ad437d4ea3d 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -9842,6 +9843,7 @@ void __init sched_init_smp(void) > > init_sched_rt_class(); > init_sched_dl_class(); > + init_sched_fair_class_late(); > > sched_smp_initialized = true; > } > @@ -12854,3 +12999,34 @@ __init void init_sched_fair_class(void) > #endif /* SMP */ > > } > + > +__init void init_sched_fair_class_late(void) > +{ > +#ifdef CONFIG_SMP > + int i; > + struct shared_runq *shared_runq; > + struct rq *rq; > + struct rq *llc_rq; > + > + for_each_possible_cpu(i) { > + if (per_cpu(sd_llc_id, i) == i) { > + llc_rq = cpu_rq(i); > + > + shared_runq = kzalloc_node(sizeof(struct shared_runq), > + GFP_KERNEL, cpu_to_node(i)); > + INIT_LIST_HEAD(&shared_runq->list); > + spin_lock_init(&shared_runq->lock); > + llc_rq->cfs.shared_runq = shared_runq; > + } > + } > + > + for_each_possible_cpu(i) { > + rq = cpu_rq(i); > + llc_rq = cpu_rq(per_cpu(sd_llc_id, i)); > + > + if (rq == llc_rq) > + continue; > + rq->cfs.shared_runq = llc_rq->cfs.shared_runq; > + } > +#endif /* SMP */ > +} I don't think this is right; the llc_id thing depends on the online mask, not on possible mask. So if you boot with a number of CPUs offline and late bring them online, you're screwy (IIRC this is actually a very common thing in virt land). Additionally, llc_id depends on the sched_domain tree, if someone were to go create partitions, they can split an LLC and llc_id would split right along with it. I think you need to move this into sched/topology.c and handle hotplug / domain (re) creation. And yes, that's going to be a pain, because you might need to re-hash existing lists.