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 CCA4CC43334 for ; Wed, 20 Jul 2022 17:55:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237598AbiGTRzA (ORCPT ); Wed, 20 Jul 2022 13:55:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48832 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229738AbiGTRy6 (ORCPT ); Wed, 20 Jul 2022 13:54:58 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id A786D6249D for ; Wed, 20 Jul 2022 10:54:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1658339696; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=jsljpx5tQYboF5VldKkSEi+SbopMz0UZBpL6h+XO8gs=; b=NHIqrfsO0Q2Ep0guFWUPJti9PyILf1MmNntDqfHTmi9BMWg4RRh1WtSBnyr848Efb6Fky8 2EFD2//uiexmLc3W2KTxGI0QAU0cu0wV2wAcP2Qhd3JsiY30SsUZUJ0hoU0qGX3UOCc3pQ FF+PFQT4WTzUy1sQu5y1ChdXu6GbrR0= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-115-33phez4DOQia0Y4TSSYSeQ-1; Wed, 20 Jul 2022 13:54:51 -0400 X-MC-Unique: 33phez4DOQia0Y4TSSYSeQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 6962F29ABA0A; Wed, 20 Jul 2022 17:54:51 +0000 (UTC) Received: from fuller.cnet (ovpn-112-4.gru2.redhat.com [10.97.112.4]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2F7881121314; Wed, 20 Jul 2022 17:54:51 +0000 (UTC) Received: by fuller.cnet (Postfix, from userid 1000) id 40CE5416CD79; Wed, 20 Jul 2022 14:54:32 -0300 (-03) Date: Wed, 20 Jul 2022 14:54:32 -0300 From: Marcelo Tosatti To: Valentin Schneider Cc: linux-kernel@vger.kernel.org, Tejun Heo , Lai Jiangshan , Peter Zijlstra , Frederic Weisbecker , Juri Lelli , Phil Auld Subject: Re: [RFC PATCH] workqueue: Unbind workers before sending them to exit() Message-ID: References: <20220719165743.3409313-1-vschneid@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220719165743.3409313-1-vschneid@redhat.com> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 19, 2022 at 05:57:43PM +0100, Valentin Schneider wrote: > It has been reported that isolated CPUs can suffer from interference due to > per-CPU kworkers waking up just to die. > > A surge of workqueue activity (sleeping workfn's exacerbate this) during > initial setup can cause extra per-CPU kworkers to be spawned. Then, a > latency-sensitive task can be running merrily on an isolated CPU only to be > interrupted sometime later by a kworker marked for death (cf. > IDLE_WORKER_TIMEOUT, 5 minutes after last kworker activity). > > Affine kworkers to the wq_unbound_cpumask (which doesn't contain isolated > CPUs, cf. HK_TYPE_WQ) before waking them up after marking them with > WORKER_DIE. > > This follows the logic of CPU hot-unplug, which has been packaged into > helpers for the occasion. > > Signed-off-by: Valentin Schneider > --- > kernel/workqueue.c | 35 ++++++++++++++++++++++++++--------- > 1 file changed, 26 insertions(+), 9 deletions(-) > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > index 1ea50f6be843..0f1a25ea4924 100644 > --- a/kernel/workqueue.c > +++ b/kernel/workqueue.c > @@ -1972,6 +1972,18 @@ static struct worker *create_worker(struct worker_pool *pool) > return NULL; > } > > +static void unbind_worker(struct worker *worker) > +{ > + kthread_set_per_cpu(worker->task, -1); > + WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, wq_unbound_cpumask) < 0); > +} > + > +static void rebind_worker(struct worker *worker, struct worker_pool *pool) > +{ > + kthread_set_per_cpu(worker->task, pool->cpu); > + WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask) < 0); > +} > + > /** > * destroy_worker - destroy a workqueue worker > * @worker: worker to be destroyed > @@ -1999,6 +2011,16 @@ static void destroy_worker(struct worker *worker) > > list_del_init(&worker->entry); > worker->flags |= WORKER_DIE; > + > + /* > + * We're sending that thread off to die, so any CPU would do. This is > + * especially relevant for pcpu kworkers affined to an isolated CPU: > + * we'd rather not interrupt an isolated CPU just for a kworker to > + * do_exit(). > + */ > + if (!(worker->flags & WORKER_UNBOUND)) > + unbind_worker(worker); > + > wake_up_process(worker->task); > } > > @@ -4999,10 +5021,8 @@ static void unbind_workers(int cpu) > > raw_spin_unlock_irq(&pool->lock); > > - for_each_pool_worker(worker, pool) { > - kthread_set_per_cpu(worker->task, -1); > - WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, wq_unbound_cpumask) < 0); > - } > + for_each_pool_worker(worker, pool) > + unbind_worker(worker); > > mutex_unlock(&wq_pool_attach_mutex); > } > @@ -5027,11 +5047,8 @@ static void rebind_workers(struct worker_pool *pool) > * of all workers first and then clear UNBOUND. As we're called > * from CPU_ONLINE, the following shouldn't fail. > */ > - for_each_pool_worker(worker, pool) { > - kthread_set_per_cpu(worker->task, pool->cpu); > - WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, > - pool->attrs->cpumask) < 0); > - } > + for_each_pool_worker(worker, pool) > + rebind_worker(worker, pool); > > raw_spin_lock_irq(&pool->lock); > > -- > 2.31.1 > > Reviewed-by: Marcelo Tosatti