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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, 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 BE32BC33C9E for ; Tue, 14 Jan 2020 23:38:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8DC252075B for ; Tue, 14 Jan 2020 23:38:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="XRomDGNa" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728774AbgANXic (ORCPT ); Tue, 14 Jan 2020 18:38:32 -0500 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:35904 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728656AbgANXib (ORCPT ); Tue, 14 Jan 2020 18:38:31 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579045111; 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=GUAdJUKTIjqZ8UnAr0WHyyOOhCddPy1gM8C7ltHr6Bc=; b=XRomDGNa3xZKv3R/QV35Sx3NO0W54zG1L+h2xGDStdHLOqRoc0fJ5VAO+JFWeJalc+T4gI xVRbvBg9mfMWx16mRVzpXdBYFioLD8KlcWoqNmHPix8Gti9FZxFMwDj9atPINNWixgEGsI TCK8UjA2R/K+VksF7PnwngdsqpYwGgI= 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-359-1O9xelYaNtOOPnOOt9HTOw-1; Tue, 14 Jan 2020 18:38:30 -0500 X-MC-Unique: 1O9xelYaNtOOPnOOt9HTOw-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0EFE3801E7B; Tue, 14 Jan 2020 23:38:29 +0000 (UTC) Received: from ming.t460p (ovpn-8-16.pek2.redhat.com [10.72.8.16]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 308F67BA48; Tue, 14 Jan 2020 23:38:18 +0000 (UTC) Date: Wed, 15 Jan 2020 07:38:14 +0800 From: Ming Lei To: Thomas Gleixner Cc: Peter Xu , Juri Lelli , Ming Lei , Linux Kernel Mailing List , linux-block@vger.kernel.org Subject: Re: Kernel-managed IRQ affinity (cont) Message-ID: <20200114233814.GA6281@ming.t460p> References: <20191216195712.GA161272@xz-x1> <20191219082819.GB15731@ming.t460p> <20191219143214.GA50561@xz-x1> <20191219161115.GA18672@ming.t460p> <87eew8l7oz.fsf@nanos.tec.linutronix.de> <20200110012802.GA4501@ming.t460p> <87v9pjrtbh.fsf@nanos.tec.linutronix.de> <20200111024835.GA24575@ming.t460p> <87r202b19f.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87r202b19f.fsf@nanos.tec.linutronix.de> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Hi Thomas, On Tue, Jan 14, 2020 at 02:45:00PM +0100, Thomas Gleixner wrote: > Ming, > > Ming Lei writes: > > On Fri, Jan 10, 2020 at 08:43:14PM +0100, Thomas Gleixner wrote: > >> Ming Lei writes: > >> > That is why I try to exclude isolated CPUs from interrupt effective affinity, > >> > turns out the approach is simple and doable. > >> > >> Yes, it's doable. But it still is inconsistent behaviour. Assume the > >> following configuration: > >> > >> 8 CPUs CPU0,1 assigned for housekeeping > >> > >> With 8 queues the proposed change does nothing because each queue is > >> mapped to exactly one CPU. > > > > That is expected behavior for this RT case, given userspace won't submit > > IO from isolated CPUs. > > What is _this_ RT case? We really don't implement policy for a specific > use case. If the kernel implements a policy then it has to be generally > useful and practical. Maybe the word of 'RT case' isn't accurate, I thought isolated CPUs is only used for realtime cases, at least that is Peter's usage, maybe I was wrong. But it can be generic for all isolated CPUs cases, in which users don't want managed interrupts to disturb the isolated CPU cores. > > >> With 4 queues you get the following: > >> > >> CPU0,1 queue 0 > >> CPU2,3 queue 1 > >> CPU4,5 queue 2 > >> CPU6,7 queue 3 > >> > >> No effect on the isolated CPUs either. > >> > >> With 2 queues you get the following: > >> > >> CPU0,1,2,3 queue 0 > >> CPU4,5,6,7 queue 1 > >> > >> So here the isolated CPUs 2 and 3 get the isolation, but 4-7 > >> not. That's perhaps intended, but definitely not documented. > > > > That is intentional change, given no IO will be submitted from 4-7 > > most of times in RT case, so it is fine to select effective CPU from > > isolated CPUs in this case. As peter mentioned, IO may just be submitted > > from isolated CPUs during booting. Once the system is setup, no IO > > comes from isolated CPUs, then no interrupt is delivered to isolated > > CPUs, then meet RT's requirement. > > Again. This is a specific usecase. Is this generally applicable? As mentioned above, it can be applied for all isolated CPUs, when users don't want managed interrupts to disturb these CPU cores. > > > We can document this change somewhere. > > Yes, this needs to be documented very clearly with that command line > parameter. OK, will do that in formal post. Thanks, Ming