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 BBF05C43331 for ; Sat, 4 Apr 2020 02:31:54 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4725C206E2 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" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4725C206E2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 936C08E0008; Fri, 3 Apr 2020 22:31:53 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8E7068E0007; Fri, 3 Apr 2020 22:31:53 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7FB698E0008; Fri, 3 Apr 2020 22:31:53 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0177.hostedemail.com [216.40.44.177]) by kanga.kvack.org (Postfix) with ESMTP id 6A2588E0007 for ; Fri, 3 Apr 2020 22:31:53 -0400 (EDT) Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 39A3362C0 for ; Sat, 4 Apr 2020 02:31:53 +0000 (UTC) X-FDA: 76668597306.24.vest24_4aa6cf55d564a X-HE-Tag: vest24_4aa6cf55d564a X-Filterd-Recvd-Size: 3759 Received: from mail-il1-f196.google.com (mail-il1-f196.google.com [209.85.166.196]) by imf44.hostedemail.com (Postfix) with ESMTP for ; Sat, 4 Apr 2020 02:31:52 +0000 (UTC) Received: by mail-il1-f196.google.com with SMTP id t11so9406932ils.1 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=S0zYS70gzbOxREmToQ48eXfVPFtmDRaKyACuIpGnTdzB495QEIZpleNbZy6KMb59+U 16AIPKJk7ZoJsB/lLRwL79LZtPvBIKyoxRlivbzwQU7QIg8CjV2aRu6RCr6DawgOQaIE FpuTAEgd8ltRvhamIhXNSwG/o0nkdMlcpz2hDIns0EB8jM7LCt+0hKku6F7fkEs1kQXf Bntdn5OFio5c5vpoc98XFBSqs0i1duDes/TH/akO1/wKQ68QdInMfs5Qns6hWs0OAmgl jY8oAUfVuUHEXkiyb+prNVmpNCnfE35kstwClinyiuKlDqTT8lAyeopyJL9sGOC4/4e+ HUuw== X-Gm-Message-State: AGi0PuYihZKnUBgywv4W7XucmzYankWpyHdzENYznOvLYOUNECUdEiyH H3VilYDPuaIgMGnT18wuuzsKtCylhmmRLma9Geo= 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" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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