Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753282AbdCBONK (ORCPT ); Thu, 2 Mar 2017 09:13:10 -0500 Received: from mx1.redhat.com ([209.132.183.28]:8679 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752748AbdCBOMw (ORCPT ); Thu, 2 Mar 2017 09:12:52 -0500 From: Daniel Bristot de Oliveira To: linux-kernel@vger.kernel.org, Ingo Molnar , Peter Zijlstra Cc: Juri Lelli , Tommaso Cucinotta , Luca Abeni , Steven Rostedt , Mike Galbraith , Romulo Silva de Oliveira Subject: [PATCH V4 1/3] sched/deadline: Replenishment timer should fire in the next period Date: Thu, 2 Mar 2017 15:10:57 +0100 Message-Id: In-Reply-To: References: X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Thu, 02 Mar 2017 14:11:13 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3673 Lines: 101 Currently, the replenishment timer is set to fire at the deadline of a task. Although that works for implicit deadline tasks because the deadline is equals to the begin of the next period, that is not correct for constrained deadline tasks (deadline < period). For instance: f.c: --------------- %< --------------- int main (void) { for(;;); } --------------- >% --------------- # gcc -o f f.c # trace-cmd record -e sched:sched_switch \ -e syscalls:sys_exit_sched_setattr \ chrt -d --sched-runtime 490000000 \ --sched-deadline 500000000 \ --sched-period 1000000000 0 ./f # trace-cmd report | grep "{pid of ./f}" After setting parameters, the task is replenished and continue running until being throttled. f-11295 [003] 13322.113776: sys_exit_sched_setattr: 0x0 The task is throttled after running 492318 ms, as expected. f-11295 [003] 13322.606094: sched_switch: f:11295 [-1] R ==> \ watchdog/3:32 [0] But then, the task is replenished 500719 ms after the first replenishment: -0 [003] 13322.614495: sched_switch: swapper/3:0 [120] R \ ==> f:11295 [-1] Running for 490277 ms: f-11295 [003] 13323.104772: sched_switch: f:11295 [-1] R ==> \ swapper/3:0 [120] Hence, in the first period, the task runs 2 * runtime, and that is a bug. During the first replenishment, the next deadline is set one period away. So the runtime / period starts to be respected. However, as the second replenishment took place in the wrong instant, the next replenishment will also be held in a wrong instant of time. Rather than occurring in the nth period away from the first activation, it is taking place in the (nth period - relative deadline). Signed-off-by: Daniel Bristot de Oliveira Reviewed-by: Luca Abeni Reviewed-by: Steven Rostedt (VMware) Reviewed-by: Juri Lelli Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Juri Lelli Cc: Tommaso Cucinotta Cc: Luca Abeni Cc: Steven Rostedt Cc: Mike Galbraith Cc: Romulo Silva de Oliveira Cc: Daniel Bristot de Oliveira Cc: linux-kernel@vger.kernel.org --- kernel/sched/deadline.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 27737f3..3e3caae 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -505,10 +505,15 @@ static void update_dl_entity(struct sched_dl_entity *dl_se, } } +static inline u64 dl_next_period(struct sched_dl_entity *dl_se) +{ + return dl_se->deadline - dl_se->dl_deadline + dl_se->dl_period; +} + /* * If the entity depleted all its runtime, and if we want it to sleep * while waiting for some new execution time to become available, we - * set the bandwidth enforcement timer to the replenishment instant + * set the bandwidth replenishment timer to the replenishment instant * and try to activate it. * * Notice that it is important for the caller to know if the timer @@ -530,7 +535,7 @@ static int start_dl_timer(struct task_struct *p) * that it is actually coming from rq->clock and not from * hrtimer's time base reading. */ - act = ns_to_ktime(dl_se->deadline); + act = ns_to_ktime(dl_next_period(dl_se)); now = hrtimer_cb_get_time(timer); delta = ktime_to_ns(now) - rq_clock(rq); act = ktime_add_ns(act, delta); -- 2.9.3