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=-7.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 A4300C433DB for ; Thu, 28 Jan 2021 17:37:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7C50664E15 for ; Thu, 28 Jan 2021 17:37:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233224AbhA1RhU (ORCPT ); Thu, 28 Jan 2021 12:37:20 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:46148 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233170AbhA1RhP (ORCPT ); Thu, 28 Jan 2021 12:37:15 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1611855349; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=TWWXXrKtDvXCZYJdS454rtlLyStjMZruwt0GmOtcIHc=; b=Mn3bYytbJ5oYbMtlAMOxXDJC7Nr+6KoeTMZdSigvWp1B6KosnjybYAXbJWNuAoGa8a+FVH /Ct0Wi1F07Q8cnoqK426N4i75j6cx6V+6P6izQ5KJ7e+AHlihf3XFmQYQpUn6DVFkiMtIM tPpyDZqVMG9Kc4yfCm14woB8NquC1fU= 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-476-boJcy9VeNuyehTGpv1lUnw-1; Thu, 28 Jan 2021 12:35:47 -0500 X-MC-Unique: boJcy9VeNuyehTGpv1lUnw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 741C784A5E0; Thu, 28 Jan 2021 17:35:44 +0000 (UTC) Received: from [10.10.113.213] (ovpn-113-213.rdu2.redhat.com [10.10.113.213]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0012310016DB; Thu, 28 Jan 2021 17:35:36 +0000 (UTC) Subject: Re: [Patch v4 1/3] lib: Restrict cpumask_local_spread to houskeeping CPUs To: Marcelo Tosatti , Thomas Gleixner Cc: Robin Murphy , 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, 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 References: <20200625223443.2684-1-nitesh@redhat.com> <20200625223443.2684-2-nitesh@redhat.com> <3e9ce666-c9cd-391b-52b6-3471fe2be2e6@arm.com> <20210127121939.GA54725@fuller.cnet> <87r1m5can2.fsf@nanos.tec.linutronix.de> <20210128165903.GB38339@fuller.cnet> From: Nitesh Narayan Lal Organization: Red Hat Inc, Message-ID: <3f138a52-7e6a-2c40-23f7-33515893a178@redhat.com> Date: Thu, 28 Jan 2021 12:35:35 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <20210128165903.GB38339@fuller.cnet> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On 1/28/21 11:59 AM, Marcelo Tosatti wrote: > On Thu, Jan 28, 2021 at 05:02:41PM +0100, Thomas Gleixner wrote: >> On Wed, Jan 27 2021 at 09:19, Marcelo Tosatti wrote: >>> On Wed, Jan 27, 2021 at 11:57:16AM +0000, Robin Murphy wrote: >>>>> + 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. >> The whole pile wants to be reverted. It's simply broken in several ways. > I was asking for your comments on interaction with CPU hotplug :-) > Anyway... > > So housekeeping_cpumask has multiple meanings. In this case: > > HK_FLAG_DOMAIN | HK_FLAG_MANAGED_IRQ > > domain > Isolate from the general SMP balancing and scheduling > algorithms. Note that performing domain isolation this way > is irreversible: it's not possible to bring back a CPU to > the domains once isolated through isolcpus. It's strongly > advised to use cpusets instead to disable scheduler load > balancing through the "cpuset.sched_load_balance" file. > It offers a much more flexible interface where CPUs can > move in and out of an isolated set anytime. > > You can move a process onto or off an "isolated" CPU via > the CPU affinity syscalls or cpuset. > begins at 0 and the maximum value is > "number of CPUs in system - 1". > > managed_irq > > Isolate from being targeted by managed interrupts > which have an interrupt mask containing isolated > CPUs. The affinity of managed interrupts is > handled by the kernel and cannot be changed via > the /proc/irq/* interfaces. > > This isolation is best effort and only effective > if the automatically assigned interrupt mask of a > device queue contains isolated and housekeeping > CPUs. If housekeeping CPUs are online then such > interrupts are directed to the housekeeping CPU > so that IO submitted on the housekeeping CPU > cannot disturb the isolated CPU. > > If a queue's affinity mask contains only isolated > CPUs then this parameter has no effect on the > interrupt routing decision, though interrupts are > only delivered when tasks running on those > isolated CPUs submit IO. IO submitted on > housekeeping CPUs has no influence on those > queues. > > So as long as the meaning of the flags are respected, seems > alright. > > Nitesh, is there anything preventing this from being fixed > in userspace ? (as Thomas suggested previously). I think it should be doable atleast for most of the devices. However, I do wonder if there is a better way of fixing this generically from the kernel? Currently, as Thomas mentioned housekeeping_cpumask() is used at different locations just to fix the issue corresponding to that component or driver. -- Thanks Nitesh