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 X-Spam-Level: X-Spam-Status: No, score=-13.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4530CC43331 for ; Wed, 25 Mar 2020 11:48:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 106D920714 for ; Wed, 25 Mar 2020 11:48:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="PAmB01Le" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727286AbgCYLsG (ORCPT ); Wed, 25 Mar 2020 07:48:06 -0400 Received: from us-smtp-delivery-74.mimecast.com ([63.128.21.74]:24648 "EHLO us-smtp-delivery-74.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726276AbgCYLsG (ORCPT ); Wed, 25 Mar 2020 07:48:06 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1585136884; 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=yVztRHM0wPS4jPDaBQT2Oc6LcCZfd2nVYB+shZ5fKfA=; b=PAmB01LeDIcjNIOsvcPFYUFigczpFiZUAe5kKJFvjpThD1GLs4vBVZDalYnDDQsHa62R0m St1vT0hYSEj3TTuR2F6xVH2baBk15Ko753F25IWKOrk5x3iM/EWeBoF55ZHFkNR5Dbpm9a CUUWS7SEyYL0kSul8jC3/G5x86Kgssk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-348-gSUD7jFQPMSXnFIah7RC5A-1; Wed, 25 Mar 2020 07:48:00 -0400 X-MC-Unique: gSUD7jFQPMSXnFIah7RC5A-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C2CC6800D5C; Wed, 25 Mar 2020 11:47:58 +0000 (UTC) Received: from fuller.cnet (ovpn-116-46.gru2.redhat.com [10.97.116.46]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 510F7BBBC2; Wed, 25 Mar 2020 11:47:58 +0000 (UTC) Received: by fuller.cnet (Postfix, from userid 1000) id 6CCC24198B04; Wed, 25 Mar 2020 08:47:36 -0300 (-03) Date: Wed, 25 Mar 2020 08:47:36 -0300 From: Marcelo Tosatti To: Frederic Weisbecker Cc: Thomas Gleixner , Chris Friesen , linux-kernel@vger.kernel.org, Christoph Lameter , Jim Somerville , Andrew Morton , Frederic Weisbecker , Peter Zijlstra Subject: Re: [PATCH v2] isolcpus: affine kernel threads to specified cpumask Message-ID: <20200325114736.GA17165@fuller.cnet> References: <20200323135414.GA28634@fuller.cnet> <87k13boxcn.fsf@nanos.tec.linutronix.de> <87imiuq0cg.fsf@nanos.tec.linutronix.de> <20200324152016.GA25422@fuller.cnet> <20200325002956.GC20223@lenoir> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200325002956.GC20223@lenoir> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Frederic, On Wed, Mar 25, 2020 at 01:30:00AM +0100, Frederic Weisbecker wrote: > On Tue, Mar 24, 2020 at 12:20:16PM -0300, Marcelo Tosatti wrote: > > > > This is a kernel enhancement to configure the cpu affinity of kernel > > threads via kernel boot option isolcpus=no_kthreads,, > > > > When this option is specified, the cpumask is immediately applied upon > > thread launch. This does not affect kernel threads that specify cpu > > and node. > > > > This allows CPU isolation (that is not allowing certain threads > > to execute on certain CPUs) without using the isolcpus=domain parameter, > > making it possible to enable load balancing on such CPUs > > during runtime (see > > > > Note-1: this is based off on Wind River's patch at > > https://github.com/starlingx-staging/stx-integ/blob/master/kernel/kernel-std/centos/patches/affine-compute-kernel-threads.patch > > > > Difference being that this patch is limited to modifying > > kernel thread cpumask: Behaviour of other threads can > > be controlled via cgroups or sched_setaffinity. > > > > Note-2: MontaVista's patch was based off Christoph Lameter's patch at > > https://lwn.net/Articles/565932/ with the only difference being > > the kernel parameter changed from kthread to kthread_cpus. > > > > Signed-off-by: Marcelo Tosatti > > I'm wondering, why do you need such a boot shift at all when you > can actually affine kthreads on runtime? New, unbound kernel threads inherit the cpumask of kthreadd. Therefore there is a race between kernel thread creation and affine. If you know of a solution to that problem, that can be used instead. > > > > --- > > > > v2: use isolcpus= subcommand (Thomas Gleixner) > > > > Documentation/admin-guide/kernel-parameters.txt | 8 ++++++++ > > include/linux/cpumask.h | 5 +++++ > > include/linux/sched/isolation.h | 1 + > > init/main.c | 1 + > > kernel/cpu.c | 13 +++++++++++++ > > kernel/kthread.c | 4 ++-- > > kernel/sched/isolation.c | 6 ++++++ > > 7 files changed, 36 insertions(+), 2 deletions(-) > > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > > index c07815d230bc..7318e3057383 100644 > > --- a/Documentation/admin-guide/kernel-parameters.txt > > +++ b/Documentation/admin-guide/kernel-parameters.txt > > @@ -1959,6 +1959,14 @@ > > the CPU affinity syscalls or cpuset. > > begins at 0 and the maximum value is > > "number of CPUs in system - 1". > > + When using cpusets, use the isolcpus option no_kthreads > > + to avoid creation of kernel threads on isolated CPUs. > > + > > + no_kthreads > > + Adjust the CPU affinity mask of unbound kernel threads to > > + not contain CPUs on the isolated list. This complements > > + the isolation provided by the cpusets mechanism described > > + above. > > Actually that should be "kthread" instead of no_kthreads. A flag of isolcpus > describes what we want a set of CPUs to be isolated from. Well, at least that's > how we started with "domain" and "managed_irq". Sure. > > > > > managed_irq > > > > diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h > > index 0fbcbacd1b29..d002332d00eb 100644 > > --- a/include/linux/sched/isolation.h > > +++ b/include/linux/sched/isolation.h > > @@ -14,6 +14,7 @@ enum hk_flags { > > HK_FLAG_DOMAIN = (1 << 5), > > HK_FLAG_WQ = (1 << 6), > > HK_FLAG_MANAGED_IRQ = (1 << 7), > > + HK_FLAG_NO_KTHREADS = (1 << 8), > > Similarly that should be HK_FLAG_KTHREAD. Sure. > > > }; > > > > #ifdef CONFIG_CPU_ISOLATION > > diff --git a/kernel/kthread.c b/kernel/kthread.c > > index b262f47046ca..be9c8d53a986 100644 > > --- a/kernel/kthread.c > > +++ b/kernel/kthread.c > > @@ -347,7 +347,7 @@ struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data), > > * The kernel thread should not inherit these properties. > > */ > > sched_setscheduler_nocheck(task, SCHED_NORMAL, ¶m); > > - set_cpus_allowed_ptr(task, cpu_all_mask); > > + set_cpus_allowed_ptr(task, cpu_kthread_mask); > > I'm wondering, why are we using cpu_all_mask and not cpu_possible_mask here? > If we used the latter, you wouldn't need to create cpu_kthread_mask and > you could directly rely on housekeeping_cpumask(HK_FLAG_KTHREAD). I suppose that either work: CPUs can only be online from cpu_possible_mask (and is contained in cpu_possible_mask). Nice cleanup, thanks. > > > diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c > > index 008d6ac2342b..e9d48729efd4 100644 > > --- a/kernel/sched/isolation.c > > +++ b/kernel/sched/isolation.c > > @@ -169,6 +169,12 @@ static int __init housekeeping_isolcpus_setup(char *str) > > continue; > > } > > > > + if (!strncmp(str, "no_kthreads,", 12)) { > > + str += 12; > > + flags |= HK_FLAG_NO_KTHREADS; > > You will certainly want HK_FLAG_WQ as well since workqueue has its own > way to deal with unbound affinity. Yep. HK_FLAG_WQ is simply a convenience so that the user does not have to configure this separately: OK. > > > + continue; > > + } > > + > > pr_warn("isolcpus: Error, unknown flag\n"); > > return 0; > > } > > > > Thanks.