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 332B3C6FD1C for ; Sat, 25 Mar 2023 22:09:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231764AbjCYWJU (ORCPT ); Sat, 25 Mar 2023 18:09:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51362 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230237AbjCYWJT (ORCPT ); Sat, 25 Mar 2023 18:09:19 -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 ESMTPS id C6DB23C0B for ; Sat, 25 Mar 2023 15:08:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1679782103; 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=gfpzCVb7RjReIdPdxbxCD31KhV4soJYjxsJSs2syVzk=; b=XkXySQxTXOCDp/KTbZtXRLpcv7diNpNAJFLi21eYNbFD+OMSoW9GD9Cq83TCp17sSxz8Yu t5YAmnpwg3YrEJtK5RnZkKS6HClShX2FYf9dpwbWIyBeey1igGYRh2fWqNcZztS/mZnUPH 3dtUyWILdrONrCOuHvdnEHPwlAs3xJ4= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-649-Fy9X5VztN_yL8p2Hw40nmQ-1; Sat, 25 Mar 2023 18:08:19 -0400 X-MC-Unique: Fy9X5VztN_yL8p2Hw40nmQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 5AC11811E7C; Sat, 25 Mar 2023 22:08:19 +0000 (UTC) Received: from [10.22.32.82] (unknown [10.22.32.82]) by smtp.corp.redhat.com (Postfix) with ESMTP id A8BC443FBD; Sat, 25 Mar 2023 22:08:18 +0000 (UTC) Message-ID: <17e804ea-64b5-97e1-d5fa-571157e15746@redhat.com> Date: Sat, 25 Mar 2023 18:08:18 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Subject: Re: [PATCH 3/5] cgroup/cpuset: Find another usable CPU if none found in current cpuset Content-Language: en-US To: =?UTF-8?Q?Michal_Koutn=c3=bd?= , Will Deacon Cc: Tejun Heo , Zefan Li , Johannes Weiner , Shuah Khan , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Peter Zijlstra References: <20230306200849.376804-1-longman@redhat.com> <20230306200849.376804-4-longman@redhat.com> <20230314181749.5b4k6selbgdhl3up@blackpad> <58a1a878-fa0b-285d-3e43-2b5103d3c770@redhat.com> <20230317122708.ax3m2d4zijkfdzjq@blackpad> <20230324143247.GA27199@willie-the-truck> <20230324181936.5sf6xjc5a4vacuku@blackpad> From: Waiman Long In-Reply-To: <20230324181936.5sf6xjc5a4vacuku@blackpad> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On 3/24/23 14:19, Michal Koutný wrote: > On Fri, Mar 24, 2023 at 02:32:50PM +0000, Will Deacon wrote: >> So approaches such as killing tasks or rejecting system calls tend not >> to work as well, since you inevitably get divergent behaviour leading >> to functional breakage rather than e.g. performance anomalies. > What about temporary performance drop from 100% to 0% aka freezing the > tasks for the duration of the mismatching affinity config? That can be a lot of extra work to freeze it. I will prefer something simpler. Without this patch, I believe it will lead to a cpumask of 0 which will cause the scheduler to pick a fallback cpu. It looks like the fallback code may be able to pick up the right cpu or it may panic the system (less likely). Cheers, Longman > > >> Having said that, the behaviour we currently have in mainline seems to >> be alright, so please don't go out of your way to accomodate these SoCs. > I see. (Just wondering what you think about the fourth option above.) > > Thanks, > Michal