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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=ham 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 86B6FC3F2D6 for ; Fri, 6 Mar 2020 07:02:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 62AAC2072A for ; Fri, 6 Mar 2020 07:02:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726245AbgCFHCK (ORCPT ); Fri, 6 Mar 2020 02:02:10 -0500 Received: from lucky1.263xmail.com ([211.157.147.133]:36518 "EHLO lucky1.263xmail.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725905AbgCFHCJ (ORCPT ); Fri, 6 Mar 2020 02:02:09 -0500 Received: from localhost (unknown [192.168.167.209]) by lucky1.263xmail.com (Postfix) with ESMTP id DB3999F894; Fri, 6 Mar 2020 15:01:41 +0800 (CST) X-MAIL-AUTO: 1 X-MAIL-GRAY: 0 X-MAIL-DELIVERY: 1 X-ADDR-CHECKED4: 1 X-ANTISPAM-LEVEL: 2 X-ABS-CHECKED: 0 Received: from localhost.localdomain (unknown [58.22.7.114]) by smtp.263.net (postfix) whith ESMTP id P32633T140274261014272S1583478094758456_; Fri, 06 Mar 2020 15:01:41 +0800 (CST) X-IP-DOMAINF: 1 X-UNIQUE-TAG: <72df5637c48843ecbb6e3b09abe72a59> X-RL-SENDER: cl@rock-chips.com X-SENDER: cl@rock-chips.com X-LOGIN-NAME: cl@rock-chips.com X-FST-TO: heiko@sntech.de X-SENDER-IP: 58.22.7.114 X-ATTACHMENT-NUM: 0 X-DNS-TYPE: 0 X-System-Flag: 0 From: To: heiko@sntech.de Cc: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, akpm@linux-foundation.org, tglx@linutronix.de, mpe@ellerman.id.au, surenb@google.com, ben.dooks@codethink.co.uk, anshuman.khandual@arm.com, catalin.marinas@arm.com, will@kernel.org, keescook@chromium.org, luto@amacapital.net, wad@chromium.org, mark.rutland@arm.com, geert+renesas@glider.be, george_davis@mentor.com, sudeep.holla@arm.com, linux@armlinux.org.uk, gregkh@linuxfoundation.org, info@metux.net, kstewart@linuxfoundation.org, allison@lohutok.net, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, huangtao@rock-chips.com, Liang Chen Subject: [PATCH v3 1/1] kthread: do not preempt current task if it is going to call schedule() Date: Fri, 6 Mar 2020 15:01:33 +0800 Message-Id: <20200306070133.18335-2-cl@rock-chips.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200306070133.18335-1-cl@rock-chips.com> References: <20200306070133.18335-1-cl@rock-chips.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Liang Chen when we create a kthread with ktrhead_create_on_cpu(),the child thread entry is ktread.c:ktrhead() which will be preempted by the parent after call complete(done) while schedule() is not called yet,then the parent will call wait_task_inactive(child) but the child is still on the runqueue, so the parent will schedule_hrtimeout() for 1 jiffy,it will waste a lot of time,especially on startup. parent child ktrhead_create_on_cpu() wait_fo_completion(&done) -----> ktread.c:ktrhead() |----- complete(done);--wakeup and preempted by parent kthread_bind() <------------| |-> schedule();--dequeue here wait_task_inactive(child) | schedule_hrtimeout(1 jiffy) -| So we hope the child just wakeup parent but not preempted by parent, and the child is going to call schedule() soon,then the parent will not call schedule_hrtimeout(1 jiffy) as the child is already dequeue. The same issue for ktrhead_park()&&kthread_parkme(). This patch can save 120ms on rk312x startup with CONFIG_HZ=300. Signed-off-by: Liang Chen --- kernel/kthread.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/kernel/kthread.c b/kernel/kthread.c index b262f47046ca..bfbfa481be3a 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -199,8 +199,15 @@ static void __kthread_parkme(struct kthread *self) if (!test_bit(KTHREAD_SHOULD_PARK, &self->flags)) break; + /* + * Thread is going to call schedule(), do not preempt it, + * or the caller of kthread_park() may spend more time in + * wait_task_inactive(). + */ + preempt_disable(); complete(&self->parked); - schedule(); + schedule_preempt_disabled(); + preempt_enable(); } __set_current_state(TASK_RUNNING); } @@ -245,8 +252,14 @@ static int kthread(void *_create) /* OK, tell user we're spawned, wait for stop or wakeup */ __set_current_state(TASK_UNINTERRUPTIBLE); create->result = current; + /* + * Thread is going to call schedule(), do not preempt it, + * or the creator may spend more time in wait_task_inactive(). + */ + preempt_disable(); complete(done); - schedule(); + schedule_preempt_disabled(); + preempt_enable(); ret = -EINTR; if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) { -- 2.17.1