From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161624AbbEEL5o (ORCPT ); Tue, 5 May 2015 07:57:44 -0400 Received: from m15-113.126.com ([220.181.15.113]:60405 "EHLO m15-113.126.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161533AbbEEL5g (ORCPT ); Tue, 5 May 2015 07:57:36 -0400 From: Xunlei Pang To: linux-kernel@vger.kernel.org Cc: Peter Zijlstra , Steven Rostedt , Juri Lelli , Ingo Molnar , Xunlei Pang Subject: [PATCH v2 2/2] sched/rt: Remove redundant conditions from task_woken_rt() Date: Tue, 5 May 2015 19:56:08 +0800 Message-Id: <1430826968-10251-2-git-send-email-xlpang@126.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1430826968-10251-1-git-send-email-xlpang@126.com> References: <1430826968-10251-1-git-send-email-xlpang@126.com> X-CM-TRANSID: DcmowAC3Pkvcr0hVjmw4Ag--.12078S3 X-Coremail-Antispam: 1Uf129KBjvJXoW7AF1kKw1UJr4UGFyruF15urg_yoW8KrWkpa 1vkrWUWF1kJa4aq3Z3trn7Xry5Ja1kJw15WFn3trWUCr45Gr1FvFWFgFyfWr1Y9r1FyF42 9FW8KayfG3WUtFJanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07jlc_3UUUUU= X-Originating-IP: [210.21.223.3] X-CM-SenderInfo: p0ost0bj6rjloofrz/1tbiJxbwv01sBkNuBgAAsy Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Xunlei Pang - Remove "has_pushable_tasks(rq)". Because for queued p, "!task_running(rq, p)" and "p->nr_cpus_allowed > 1" already imply that "has_pushable_tasks(rq)" is true. - Remove "!test_tsk_need_resched(rq->curr)". The condtion mainly intends to ensure higher priority rt tasks won't be pushed away. I can think of two reasons below for getting rid of it. 1) With following "rq->curr->prio <= p->prio", we still can guarantee that purpose. "rq->curr->prio <= p->prio" implies the "need resched flag" wasn't set by check_preempt_curr() except the one set by check_preempt_equal_prio() for equal prio cases(In this case, if the condition is removed, it may result in an extra push_rt_tasks(), but this doesn't cause the wrong logic, in fact this extra push_rt_tasks() will probably return quickly for the case). Addtionally, there're also cases the "need resched flag" got set before the waking, with current implementation it needn't to push lower priority tasks as the cpu will schedule, while it will do an extra pushing if the condition is removed. But on the other hand, we can get a timely pushing for the woken tasks after the condition is removed(better for the non-preemptible kernel). 2) With following condtion "rq->curr->nr_cpus_allowed < 2" which was added by commit b3bc211cfe7d ("sched: Give CPU bound RT tasks preference"). But in the scenario descibed in the commit, "need resched flag" was already set before in check_preempt_curr(), thus "!test_tsk_need_resched(rq->curr)" is always false which means with current implementation the commit is futile for task_woken_rt(). So, by removing this condition, we get the right logic. Signed-off-by: Xunlei Pang --- v1->v2: Improved the changelog. kernel/sched/rt.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 4176f33..95b596b 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -2232,8 +2232,6 @@ out: static void task_woken_rt(struct rq *rq, struct task_struct *p) { if (!task_running(rq, p) && - !test_tsk_need_resched(rq->curr) && - has_pushable_tasks(rq) && p->nr_cpus_allowed > 1 && (dl_task(rq->curr) || rt_task(rq->curr)) && (rq->curr->nr_cpus_allowed < 2 || -- 1.9.1