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 0C585C00140 for ; Mon, 15 Aug 2022 13:52:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232717AbiHONwj (ORCPT ); Mon, 15 Aug 2022 09:52:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36494 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229994AbiHONwg (ORCPT ); Mon, 15 Aug 2022 09:52:36 -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 ESMTP id 46BD9CE32 for ; Mon, 15 Aug 2022 06:52:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1660571553; 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=A0Oy07t9HeUyM/chaHP6TWWJCl778sh8kflz1rnE6aw=; b=eDnA3d+heaobCI949ZPWjhndOz0O/Zl8eOVMDAXSAtrjy/EoNPOAiSbGKMmnRrjAs6suSb 0KQjM+7Xe46x09zLDxYxV/7ywTdqNpWqzSAGT/m2XOe5LKW9SOwsnRPQHbNcgUbO6r3oHh dKo1P/9I9rMxTsG3nzfuw1MDDIImuh8= 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-327-PUbTJFO-OteY8AhLfq8DEw-1; Mon, 15 Aug 2022 09:52:29 -0400 X-MC-Unique: PUbTJFO-OteY8AhLfq8DEw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id C74CB101A592; Mon, 15 Aug 2022 13:52:28 +0000 (UTC) Received: from [10.18.17.215] (dhcp-17-215.bos.redhat.com [10.18.17.215]) by smtp.corp.redhat.com (Postfix) with ESMTP id DB5002166B29; Mon, 15 Aug 2022 13:52:27 +0000 (UTC) Message-ID: <401bae73-3063-e0ab-c288-2c6e3be75fc5@redhat.com> Date: Mon, 15 Aug 2022 09:52:27 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH v3 1/3] sched: Use user_cpus_ptr for saving user provided cpumask in sched_setaffinity() Content-Language: en-US To: Peter Zijlstra Cc: Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider , Tejun Heo , Zefan Li , Johannes Weiner , Will Deacon , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Linus Torvalds References: <20220812203929.364341-1-longman@redhat.com> <20220812203929.364341-2-longman@redhat.com> From: Waiman Long In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/15/22 04:57, Peter Zijlstra wrote: > On Fri, Aug 12, 2022 at 04:39:27PM -0400, Waiman Long wrote: >> The user_cpus_ptr field is added by commit b90ca8badbd1 ("sched: >> Introduce task_struct::user_cpus_ptr to track requested affinity"). It >> is currently used only by arm64 arch due to possible asymmetric cpu >> setup. This patch extends its usage to save user provided cpumask when >> sched_setaffinity() is called for all arches. >> >> To preserve the existing arm64 use case, a new cpus_affinity_set flag is >> added to differentiate if user_cpus_ptr is set up by sched_setaffinity() >> or by force_compatible_cpus_allowed_ptr(). user_cpus_ptr >> set by sched_setaffinity() has priority and won't be >> overwritten by force_compatible_cpus_allowed_ptr() or >> relax_compatible_cpus_allowed_ptr(). > What why ?! The only possible case where > restrict_cpus_allowed_ptr() will now need that weird new state is when > the affinity has never been set before, in that case cpus_ptr should be > possible_mask. Since I don't have a full history for this particular patch series that add user_cpus_ptr, I am hesitant to change the current behavior for arm64 systems. However, given the statement that user_cpus_ptr is for tracking "requested affinity" which I assume is when user applications call sched_setaffinity(). It does make sense we may not really need this if sched_setaffinity() is never called. > Please just make a single consistent rule and don't make weird corner > cases like this. I will take a closer look to try to simplify the rule here. Cheers, Longman