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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 5CCA9C1B0D8 for ; Mon, 7 Dec 2020 21:25:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2A383221FA for ; Mon, 7 Dec 2020 21:25:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727416AbgLGVZf (ORCPT ); Mon, 7 Dec 2020 16:25:35 -0500 Received: from mga04.intel.com ([192.55.52.120]:3683 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725774AbgLGVZf (ORCPT ); Mon, 7 Dec 2020 16:25:35 -0500 IronPort-SDR: PzKWmiwReFtVwJ9TpbcPtlPF51IBLx4u465/Zu2YQBXQiUr+C2q21h3SizR51j9x8l/F4ByxiR G+UDCHEp9v+A== X-IronPort-AV: E=McAfee;i="6000,8403,9828"; a="171207577" X-IronPort-AV: E=Sophos;i="5.78,400,1599548400"; d="scan'208";a="171207577" Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Dec 2020 13:24:54 -0800 IronPort-SDR: N/28dJUJNMCdJSszU2y/GklgeDWZuupTNFrDjIll6ESPmRcvHXN3YvNatn9tUolilbsIYqK7/b Xu1bc6jrBy0A== X-IronPort-AV: E=Sophos;i="5.78,400,1599548400"; d="scan'208";a="437100464" Received: from rchatre-mobl3.amr.corp.intel.com (HELO [10.209.61.193]) ([10.209.61.193]) by fmsmga001-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Dec 2020 13:24:52 -0800 Subject: Re: [PATCH 1/3] x86/resctrl: Move setting task's active CPU in a mask into helpers To: Borislav Petkov Cc: tglx@linutronix.de, fenghua.yu@intel.com, tony.luck@intel.com, kuo-lang.tseng@intel.com, shakeelb@google.com, valentin.schneider@arm.com, mingo@redhat.com, babu.moger@amd.com, james.morse@arm.com, hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <77973e75a10bf7ef9b33c664544667deee9e1a8e.1607036601.git.reinette.chatre@intel.com> <20201207182912.GF20489@zn.tnic> From: Reinette Chatre Message-ID: Date: Mon, 7 Dec 2020 13:24:51 -0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: <20201207182912.GF20489@zn.tnic> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Borislav, Thank you very much for your review. On 12/7/2020 10:29 AM, Borislav Petkov wrote: > On Thu, Dec 03, 2020 at 03:25:48PM -0800, Reinette Chatre wrote: >> From: Fenghua Yu >> >> The code of setting the CPU on which a task is running in a CPU mask is >> moved into a couple of helpers. > > Pls read section "2) Describe your changes" in > Documentation/process/submitting-patches.rst for more details. > > More specifically: > > "Describe your changes in imperative mood, e.g. "make xyzzy do frotz" > instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy > to do frotz", as if you are giving orders to the codebase to change > its behaviour." > >> The new helper task_on_cpu() will be reused shortly. > > "reused shortly"? I don't think so. How about: "Move the setting of the CPU on which a task is running in a CPU mask into a couple of helpers. There is no functional change. This is a preparatory change for the fix in the following patch from where the Fixes tag is copied." > >> >> Signed-off-by: Fenghua Yu >> Signed-off-by: Reinette Chatre >> Reviewed-by: Tony Luck >> Cc: stable@vger.kernel.org > > Fixes? > > I guess the same commit from the other two: > > Fixes: e02737d5b826 ("x86/intel_rdt: Add tasks files") > > ? Correct. I will add it. The addition to the commit message above aims to explain a Fixes tag to a patch with no functional changes. >> --- >> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 47 +++++++++++++++++++------- >> 1 file changed, 34 insertions(+), 13 deletions(-) >> >> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c >> index 6f4ca4bea625..68db7d2dec8f 100644 >> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c >> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c >> @@ -525,6 +525,38 @@ static void rdtgroup_remove(struct rdtgroup *rdtgrp) >> kfree(rdtgrp); >> } >> >> +#ifdef CONFIG_SMP >> +/* Get the CPU if the task is on it. */ >> +static bool task_on_cpu(struct task_struct *t, int *cpu) >> +{ >> + /* >> + * This is safe on x86 w/o barriers as the ordering of writing to >> + * task_cpu() and t->on_cpu is reverse to the reading here. The >> + * detection is inaccurate as tasks might move or schedule before >> + * the smp function call takes place. In such a case the function >> + * call is pointless, but there is no other side effect. >> + */ >> + if (t->on_cpu) { >> + *cpu = task_cpu(t); > > Why have an I/O parameter when you can make it simply: > > static int task_on_cpu(struct task_struct *t) > { > if (t->on_cpu) > return task_cpu(t); > > return -1; > } > >> + >> + return true; >> + } >> + >> + return false; >> +} >> + >> +static void set_task_cpumask(struct task_struct *t, struct cpumask *mask) >> +{ >> + int cpu; >> + >> + if (mask && task_on_cpu(t, &cpu)) >> + cpumask_set_cpu(cpu, mask); > > And that you can turn into: > > if (!mask) > return; > > cpu = task_on_cpu(t); > if (cpu < 0) > return; > > cpumask_set_cpu(cpu, mask); > > Readable and simple. > > Hmm? > Will do. Thank you very much. Reinette