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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 30083C2BB55 for ; Thu, 16 Apr 2020 11:45:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1742A21D95 for ; Thu, 16 Apr 2020 11:45:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2506578AbgDPLpO (ORCPT ); Thu, 16 Apr 2020 07:45:14 -0400 Received: from foss.arm.com ([217.140.110.172]:59306 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2634046AbgDPLoC (ORCPT ); Thu, 16 Apr 2020 07:44:02 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id BE53DC14; Thu, 16 Apr 2020 04:44:01 -0700 (PDT) Received: from e113632-lin (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A31B73F73D; Thu, 16 Apr 2020 04:44:00 -0700 (PDT) References: <20200415210512.805-1-valentin.schneider@arm.com> <20200415210512.805-7-valentin.schneider@arm.com> <20200416104725.GM20730@hirez.programming.kicks-ass.net> User-agent: mu4e 0.9.17; emacs 26.3 From: Valentin Schneider To: Peter Zijlstra Cc: Vincent Guittot , linux-kernel , Ingo Molnar , Dietmar Eggemann , Ingo Molnar , Juri Lelli , Steven Rostedt Subject: Re: [PATCH v3 6/9] sched: Kill select_task_rq()'s sd_flag parameter In-reply-to: <20200416104725.GM20730@hirez.programming.kicks-ass.net> Date: Thu, 16 Apr 2020 12:43:54 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 16/04/20 11:47, Peter Zijlstra wrote: > On Thu, Apr 16, 2020 at 09:42:36AM +0200, Vincent Guittot wrote: >> On Wed, 15 Apr 2020 at 23:05, Valentin Schneider >> > @@ -6622,13 +6622,25 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) >> > * preempt must be disabled. >> > */ >> > static int >> > +select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags) >> > { >> > + int sync = (wake_flags & WF_SYNC) && !(current->flags & PF_EXITING); >> > struct sched_domain *tmp, *sd = NULL; >> > int cpu = smp_processor_id(); >> > int new_cpu = prev_cpu; >> > int want_affine = 0; >> > - int sync = (wake_flags & WF_SYNC) && !(current->flags & PF_EXITING); >> > + int sd_flag; >> > + >> > + switch (wake_flags & (WF_TTWU | WF_FORK | WF_EXEC)) { >> >> You remove a function parameter, which was directly set with the right >> flag, but then you add a switch case to recreate this sd_flag >> internally. Not sure we can say that it's real benefit >> >> > + case WF_TTWU: >> > + sd_flag = SD_BALANCE_WAKE; >> > + break; >> > + case WF_FORK: >> > + sd_flag = SD_BALANCE_FORK; >> > + break; >> > + default: >> > + sd_flag = SD_BALANCE_EXEC; >> > + } > > Agreed, that's a bit yuck, how about something like so instead: > Aligning the SD_* and WF_* flags sure makes it simpler, I just wasn't daring enough to do that. I suppose we'll want some BUILD_BUG_ON() checks just for good measure. Also, it doesn't directly solve the switch case of 9/9, but I may get out of it with some hackery such as what I suggested in my reply to Vincent. > > --- a/include/linux/sched/topology.h > +++ b/include/linux/sched/topology.h > @@ -11,10 +11,12 @@ > */ > #ifdef CONFIG_SMP > > +/* First nibble of SD_flag is shared with WF_flag */ > #define SD_BALANCE_NEWIDLE 0x0001 /* Balance when about to become idle */ > #define SD_BALANCE_EXEC 0x0002 /* Balance on exec */ > #define SD_BALANCE_FORK 0x0004 /* Balance on fork, clone */ > #define SD_BALANCE_WAKE 0x0008 /* Balance on wakeup */ > + > #define SD_WAKE_AFFINE 0x0010 /* Wake task to waking CPU */ > #define SD_ASYM_CPUCAPACITY 0x0020 /* Domain members have different CPU capacities */ > #define SD_SHARE_CPUCAPACITY 0x0040 /* Domain members share CPU capacity */ > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6635,16 +6635,8 @@ select_task_rq_fair(struct task_struct * > int want_affine = 0; > int sd_flag; > > - switch (wake_flags & (WF_TTWU | WF_FORK | WF_EXEC)) { > - case WF_TTWU: > - sd_flag = SD_BALANCE_WAKE; > - break; > - case WF_FORK: > - sd_flag = SD_BALANCE_FORK; > - break; > - default: > - sd_flag = SD_BALANCE_EXEC; > - } > + /* SD_flags and WF_flags share the first nibble */ > + sd_flag = wake_flags & 0xf; > > if (sd_flag & SD_BALANCE_WAKE) { > record_wakee(p); > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1685,11 +1685,12 @@ static inline int task_on_rq_migrating(s > /* > * Wake flags > */ > -#define WF_SYNC 0x01 /* Waker goes to sleep after wakeup */ > -#define WF_TTWU 0x02 /* Regular task wakeup */ > -#define WF_FORK 0x04 /* Child wakeup after fork */ > -#define WF_EXEC 0x08 /* "Fake" wakeup at exec */ > -#define WF_MIGRATED 0x10 /* Internal use, task got migrated */ > +#define WF_EXEC 0x02 /* SD_BALANCE_EXEC */ > +#define WF_FORK 0x04 /* SD_BALANCE_FORK */ > +#define WF_TTWU 0x08 /* SD_BALANCE_WAKE */ > + > +#define WF_SYNC 0x10 /* Waker goes to sleep after wakeup */ > +#define WF_MIGRATED 0x20 /* Internal use, task got migrated */ > > /* > * To aid in avoiding the subversion of "niceness" due to uneven distribution