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=-0.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 0DF1AC2BA17 for ; Sat, 4 Apr 2020 02:31:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D3940206E2 for ; Sat, 4 Apr 2020 02:31:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="VDVyVD03" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726303AbgDDCbx (ORCPT ); Fri, 3 Apr 2020 22:31:53 -0400 Received: from mail-il1-f196.google.com ([209.85.166.196]:38296 "EHLO mail-il1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726186AbgDDCbx (ORCPT ); Fri, 3 Apr 2020 22:31:53 -0400 Received: by mail-il1-f196.google.com with SMTP id n13so9389811ilm.5 for ; Fri, 03 Apr 2020 19:31:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=73jqoDJR4Hmz4eV5wHtz3Ds21ROllKQjJV/hPH99ZdQ=; b=VDVyVD036uSZxfqSuWAQxWfPYz/hc1ryWjFRuLKKKmkrG4I2N9Uc4OOCMghKZeSZdo 05vsC2nxlbYe1LIKVCaHhhrgrSFnZprq1B6P6/EgMJfwm1Rf6ZvruR5bYPhpkYfdhrvm a/8s5P0Ad2/3iJXlEbt2prcubwNr5gzhjvQ8zgZMNLKh2IfcbaueRCu0pH7eswPzPcTk zKlgXy/O9sZAR4dNEUN/SNXg5Ls7L5D3RhSKvL5zU7d8DmKFoLiYQEBkvaUNaalQ1qNn FLaac3BmihOPIWBrjSnM5RZf2jVKS/X0RhOuVcgbJS6tcLsHqG0M31BLvrOK+DICCtWN wKyQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=73jqoDJR4Hmz4eV5wHtz3Ds21ROllKQjJV/hPH99ZdQ=; b=ecAjLlfALmtiXSvflsBijXqwurE4hdGcVfNhHcgArBbw4D7XrNlqziaMxNOtSlJsXU KzzPWJrqU87KG0gov+EK9kyRkzuKPKjQPTvk9rBYGTebzhxBTuahSsjW1r55ZGHVkFv4 XZXiOs9Dn/lgQ8hdQop2FDkr/N6bAZM0+vqzq8ibPoWQUHX/f/0gdqiW3KnxwgPrSWOP NLrGfXymai8f2aa8ijG2iz/3kFBmeFzy4YNpmoYsFwQlMIwgtzN7xKZvnOZkWeWlmc6j vgdWAGiBA84A18hFoiJezK6DH+mfhSsm4+bSGNplC4yYpIXol1TYWWALe+Sia4MibUXF 72Jg== X-Gm-Message-State: AGi0PubfBuRa94nEhYxOLLsskxWzaqkTV6VD32YoU/GeKmyDJXzdds5E M2g1qWq5xf1vkNfsA9eaFaJ3ciw59swl7YQVETQ= X-Google-Smtp-Source: APiQypJhzFO86yuwD4MhRrgZWWEWwLc7RswAnaUHR2K14Xm7sNF5Vyqy0zppH197durO3VgG/RhP8JdliQMepiw57t4= X-Received: by 2002:a92:d105:: with SMTP id a5mr11645280ilb.142.1585967512259; Fri, 03 Apr 2020 19:31:52 -0700 (PDT) MIME-Version: 1.0 References: <1585904125-2819-1-git-send-email-laoar.shao@gmail.com> <20200403152016.GA69203@cmpxchg.org> In-Reply-To: <20200403152016.GA69203@cmpxchg.org> From: Yafang Shao Date: Sat, 4 Apr 2020 10:31:16 +0800 Message-ID: Subject: Re: [PATCH] psi: fix randomized calculation in record_times() To: Johannes Weiner Cc: Peter Zijlstra , Andrew Morton , Linux MM , LKML , Daniel Drake , Suren Baghdasaryan Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 3, 2020 at 11:20 PM Johannes Weiner wrote: > > On Fri, Apr 03, 2020 at 04:55:25AM -0400, Yafang Shao wrote: > > @@ -690,7 +690,10 @@ static void psi_group_change(struct psi_group *group, int cpu, > > */ > > write_seqcount_begin(&groupc->seq); > > > > - record_times(groupc, cpu, false); > > + if (groupc->total_tasks) > > + record_times(groupc, cpu, false); > > + else > > + groupc->state_start = cpu_clock(cpu); > > This change appears is a no-op. If there are no tasks, > groupc->state_mask is 0, and the only thing record_times() does is > > groupc->state_start = cpu_clock(cpu); > > Did you encounter actual problems, or are you just reading the code? No real issues. Just reading the code and found it looks like a little weird. But as you explained that state_mask can also guarantee it then we don't need to make this change. Thanks for the explanation. Thanks Yafang