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=-17.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,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 41AE8C433E9 for ; Wed, 27 Jan 2021 13:14:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 064A7207A3 for ; Wed, 27 Jan 2021 13:14:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237758AbhA0NOF (ORCPT ); Wed, 27 Jan 2021 08:14:05 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:51638 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238025AbhA0NLk (ORCPT ); Wed, 27 Jan 2021 08:11:40 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1611753014; 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=hJ4khNSatKes1oULY24OEMe4Z2NSkL2V3kH7MRO9ztw=; b=UDICIWN0AZf7Q1ScTwGmyTe9EGv9yoB6wfLhB4JCmtBZgPZeRYpPpdVy0RXNkFiQY4DF9F KSgMpfEvJgUEy2JEMNivqKfsfrYUX6GPVcAdOx/8fYJZLdUqCKq3YMjXY/fOeiIl2c2v/n Bvg49uIASGJoOhie+/LxHiboLBkX3N0= 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-423-fAnSPFvWNkicSGUsF0mlFg-1; Wed, 27 Jan 2021 08:10:13 -0500 X-MC-Unique: fAnSPFvWNkicSGUsF0mlFg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 46281801817; Wed, 27 Jan 2021 13:10:10 +0000 (UTC) Received: from fuller.cnet (ovpn-112-2.gru2.redhat.com [10.97.112.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 447115D9D5; Wed, 27 Jan 2021 13:10:02 +0000 (UTC) Received: by fuller.cnet (Postfix, from userid 1000) id C2807416D87F; Wed, 27 Jan 2021 10:09:25 -0300 (-03) Date: Wed, 27 Jan 2021 10:09:25 -0300 From: Marcelo Tosatti To: Robin Murphy , Thomas Gleixner Cc: Nitesh Narayan Lal , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, frederic@kernel.org, juri.lelli@redhat.com, abelits@marvell.com, bhelgaas@google.com, linux-pci@vger.kernel.org, rostedt@goodmis.org, mingo@kernel.org, peterz@infradead.org, tglx@linutronix.de, davem@davemloft.net, akpm@linux-foundation.org, sfr@canb.auug.org.au, stephen@networkplumber.org, rppt@linux.vnet.ibm.com, jinyuqi@huawei.com, zhangshaokun@hisilicon.com Subject: Re: [Patch v4 1/3] lib: Restrict cpumask_local_spread to houskeeping CPUs Message-ID: <20210127130925.GA64740@fuller.cnet> References: <20200625223443.2684-1-nitesh@redhat.com> <20200625223443.2684-2-nitesh@redhat.com> <3e9ce666-c9cd-391b-52b6-3471fe2be2e6@arm.com> <20210127121939.GA54725@fuller.cnet> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Wed, Jan 27, 2021 at 12:36:30PM +0000, Robin Murphy wrote: > On 2021-01-27 12:19, Marcelo Tosatti wrote: > > On Wed, Jan 27, 2021 at 11:57:16AM +0000, Robin Murphy wrote: > > > Hi, > > > > > > On 2020-06-25 23:34, Nitesh Narayan Lal wrote: > > > > From: Alex Belits > > > > > > > > The current implementation of cpumask_local_spread() does not respect the > > > > isolated CPUs, i.e., even if a CPU has been isolated for Real-Time task, > > > > it will return it to the caller for pinning of its IRQ threads. Having > > > > these unwanted IRQ threads on an isolated CPU adds up to a latency > > > > overhead. > > > > > > > > Restrict the CPUs that are returned for spreading IRQs only to the > > > > available housekeeping CPUs. > > > > > > > > Signed-off-by: Alex Belits > > > > Signed-off-by: Nitesh Narayan Lal > > > > --- > > > > lib/cpumask.c | 16 +++++++++++----- > > > > 1 file changed, 11 insertions(+), 5 deletions(-) > > > > > > > > diff --git a/lib/cpumask.c b/lib/cpumask.c > > > > index fb22fb266f93..85da6ab4fbb5 100644 > > > > --- a/lib/cpumask.c > > > > +++ b/lib/cpumask.c > > > > @@ -6,6 +6,7 @@ > > > > #include > > > > #include > > > > #include > > > > +#include > > > > /** > > > > * cpumask_next - get the next cpu in a cpumask > > > > @@ -205,22 +206,27 @@ void __init free_bootmem_cpumask_var(cpumask_var_t mask) > > > > */ > > > > unsigned int cpumask_local_spread(unsigned int i, int node) > > > > { > > > > - int cpu; > > > > + int cpu, hk_flags; > > > > + const struct cpumask *mask; > > > > + hk_flags = HK_FLAG_DOMAIN | HK_FLAG_MANAGED_IRQ; > > > > + mask = housekeeping_cpumask(hk_flags); > > > > > > AFAICS, this generally resolves to something based on cpu_possible_mask > > > rather than cpu_online_mask as before, so could now potentially return an > > > offline CPU. Was that an intentional change? > > > > Robin, > > > > AFAICS online CPUs should be filtered. > > Apologies if I'm being thick, but can you explain how? In the case of > isolation being disabled or compiled out, housekeeping_cpumask() is > literally just "return cpu_possible_mask;". If we then iterate over that > with for_each_cpu() and just return the i'th possible CPU (e.g. in the > NUMA_NO_NODE case), what guarantees that CPU is actually online? > > Robin. Nothing, but that was the situation before 1abdfe706a579a702799fce465bceb9fb01d407c as well. cpumask_local_spread() should probably be disabling CPU hotplug. Thomas? > > > > I was just looking at the current code since I had the rare presence of mind > > > to check if something suitable already existed before I start open-coding > > > "any online CPU, but local node preferred" logic for handling IRQ affinity > > > in a driver - cpumask_local_spread() appears to be almost what I want (if a > > > bit more heavyweight), if only it would actually guarantee an online CPU as > > > the kerneldoc claims :( > > > > > > Robin. > > > > > > > /* Wrap: we always want a cpu. */ > > > > - i %= num_online_cpus(); > > > > + i %= cpumask_weight(mask); > > > > if (node == NUMA_NO_NODE) { > > > > - for_each_cpu(cpu, cpu_online_mask) > > > > + for_each_cpu(cpu, mask) { > > > > if (i-- == 0) > > > > return cpu; > > > > + } > > > > } else { > > > > /* NUMA first. */ > > > > - for_each_cpu_and(cpu, cpumask_of_node(node), cpu_online_mask) > > > > + for_each_cpu_and(cpu, cpumask_of_node(node), mask) { > > > > if (i-- == 0) > > > > return cpu; > > > > + } > > > > - for_each_cpu(cpu, cpu_online_mask) { > > > > + for_each_cpu(cpu, mask) { > > > > /* Skip NUMA nodes, done above. */ > > > > if (cpumask_test_cpu(cpu, cpumask_of_node(node))) > > > > continue; > > > > > >