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, URIBL_BLOCKED,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 885B8C3F2D1 for ; Thu, 5 Mar 2020 10:00:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 62B4C21556 for ; Thu, 5 Mar 2020 10:00:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727430AbgCEKAG (ORCPT ); Thu, 5 Mar 2020 05:00:06 -0500 Received: from lucky1.263xmail.com ([211.157.147.131]:50960 "EHLO lucky1.263xmail.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726988AbgCEKAE (ORCPT ); Thu, 5 Mar 2020 05:00:04 -0500 Received: from localhost (unknown [192.168.167.8]) by lucky1.263xmail.com (Postfix) with ESMTP id 8B7BD8A264; Thu, 5 Mar 2020 17:59:59 +0800 (CST) 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 P12225T140183483700992S1583402391050204_; Thu, 05 Mar 2020 17:59:59 +0800 (CST) X-IP-DOMAINF: 1 X-UNIQUE-TAG: 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 v2 1/1] sched/fair: do not preempt current task if it is going to call schedule() Date: Thu, 5 Mar 2020 17:59:48 +0800 Message-Id: <20200305095948.10873-2-cl@rock-chips.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200305095948.10873-1-cl@rock-chips.com> References: <20200305095948.10873-1-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 --- include/linux/sched.h | 5 +++++ kernel/kthread.c | 4 ++++ kernel/sched/fair.c | 13 +++++++++++++ 3 files changed, 22 insertions(+) diff --git a/include/linux/sched.h b/include/linux/sched.h index 04278493bf15..54bf336f5790 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1533,6 +1533,7 @@ static inline bool is_percpu_thread(void) #define PFA_SPEC_IB_DISABLE 5 /* Indirect branch speculation restricted */ #define PFA_SPEC_IB_FORCE_DISABLE 6 /* Indirect branch speculation permanently restricted */ #define PFA_SPEC_SSB_NOEXEC 7 /* Speculative Store Bypass clear on execve() */ +#define PFA_GOING_TO_SCHED 8 /* task is going to call schedule() */ #define TASK_PFA_TEST(name, func) \ static inline bool task_##func(struct task_struct *p) \ @@ -1575,6 +1576,10 @@ TASK_PFA_CLEAR(SPEC_IB_DISABLE, spec_ib_disable) TASK_PFA_TEST(SPEC_IB_FORCE_DISABLE, spec_ib_force_disable) TASK_PFA_SET(SPEC_IB_FORCE_DISABLE, spec_ib_force_disable) +TASK_PFA_TEST(GOING_TO_SCHED, going_to_sched) +TASK_PFA_SET(GOING_TO_SCHED, going_to_sched) +TASK_PFA_CLEAR(GOING_TO_SCHED, going_to_sched) + static inline void current_restore_flags(unsigned long orig_flags, unsigned long flags) { diff --git a/kernel/kthread.c b/kernel/kthread.c index b262f47046ca..bc96de2648f6 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -199,8 +199,10 @@ static void __kthread_parkme(struct kthread *self) if (!test_bit(KTHREAD_SHOULD_PARK, &self->flags)) break; + task_set_going_to_sched(current); complete(&self->parked); schedule(); + task_clear_going_to_sched(current); } __set_current_state(TASK_RUNNING); } @@ -245,8 +247,10 @@ static int kthread(void *_create) /* OK, tell user we're spawned, wait for stop or wakeup */ __set_current_state(TASK_UNINTERRUPTIBLE); create->result = current; + task_set_going_to_sched(current); complete(done); schedule(); + task_clear_going_to_sched(current); ret = -EINTR; if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) { diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 3c8a379c357e..78666cec794a 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4330,6 +4330,12 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued) hrtimer_active(&rq_of(cfs_rq)->hrtick_timer)) return; #endif + /* + * current task is going to call schedule(), do not preempt it or + * it will casue more useless contex_switch(). + */ + if (task_going_to_sched(rq_of(cfs_rq)->curr)) + return; if (cfs_rq->nr_running > 1) check_preempt_tick(cfs_rq, curr); @@ -6634,6 +6640,13 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_ if (test_tsk_need_resched(curr)) return; + /* + * current task is going to call schedule(), do not preempt it or + * it will casue more useless contex_switch(). + */ + if (task_going_to_sched(curr)) + return; + /* Idle tasks are by definition preempted by non-idle tasks. */ if (unlikely(task_has_idle_policy(curr)) && likely(!task_has_idle_policy(p))) -- 2.17.1