Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759906AbaGDBmC (ORCPT ); Thu, 3 Jul 2014 21:42:02 -0400 Received: from mail-qc0-f175.google.com ([209.85.216.175]:51681 "EHLO mail-qc0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752056AbaGDBmA (ORCPT ); Thu, 3 Jul 2014 21:42:00 -0400 MIME-Version: 1.0 In-Reply-To: <20140703115037.938f4c5dcd5a110529ff0df6@gmail.com> References: <1404091570-5041-1-git-send-email-zzhsuny@gmail.com> <20140701130816.GR6758@twins.programming.kicks-ass.net> <20140701155915.55de01236e0540e1f0754560@gmail.com> <20140703115037.938f4c5dcd5a110529ff0df6@gmail.com> Date: Thu, 3 Jul 2014 21:41:59 -0400 Message-ID: Subject: Re: [PATCH] [sched] Don't account time after deadline twice From: Zhihui Zhang To: Juri Lelli Cc: Peter Zijlstra , mingo@redhat.com, linux-kernel@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org We calculate difference between two readings of a clock to see how much time has elapsed. Part of the time between rq_clock(rq) - dl_se->deadline can indeed be accounted for by reading a different clock (i.e., rq_clock_task()) if the task was running during the period. And that is how dl_se->runtime is obtained. After all, both clocks are running independently, right? Furthermore, the caller of dl_runtime_exceeded() will still use rq_clock() and dl_se->deadline to determine if we throttle or replenish. Anyway, I have failed to see any steal of time. Could you please give a concrete example (perhaps with numbers)? thanks, -Zhihui On Thu, Jul 3, 2014 at 5:50 AM, Juri Lelli wrote: > On Wed, 2 Jul 2014 19:44:04 -0400 > Zhihui Zhang wrote: > >> My point is that rq_clock(rq) - dl_se->deadline is already part of >> dl_se->runtime, which is decremented before calling dl_runtime_exceeded(). > > But, we decrement dl_se->runtime looking at rq_clock_task(rq), that is > in general <= rq_clock(rq), that we use to handle deadlines. So, if we > do like you suggest, in some cases we could end up stealing some > bandwidth from the system. Indeed, we prefer some pessimism here. > > Thanks, > > - Juri > >> So the following line is not needed in the case of both overrun and missing >> deadline: >> >> dl_se->runtime -= rq_clock(rq) - dl_se->deadline; >> >> Or did I miss anything? >> >> thanks, >> >> >> On Tue, Jul 1, 2014 at 9:59 AM, Juri Lelli wrote: >> >> > On Tue, 1 Jul 2014 15:08:16 +0200 >> > Peter Zijlstra wrote: >> > >> > > On Sun, Jun 29, 2014 at 09:26:10PM -0400, Zhihui Zhang wrote: >> > > > Unless we want to double-penalize an overrun task, the time after the >> > deadline >> > > > and before the current time is already accounted in the negative >> > dl_se->runtime >> > > > value. So we can leave it as is in the case of dmiss && rorun. >> > > >> > > Juri? >> > > >> > > > Signed-off-by: Zhihui Zhang >> > > > --- >> > > > kernel/sched/deadline.c | 6 ++---- >> > > > 1 file changed, 2 insertions(+), 4 deletions(-) >> > > > >> > > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c >> > > > index fc4f98b1..67df0d6 100644 >> > > > --- a/kernel/sched/deadline.c >> > > > +++ b/kernel/sched/deadline.c >> > > > @@ -579,10 +579,8 @@ int dl_runtime_exceeded(struct rq *rq, struct >> > sched_dl_entity *dl_se) >> > > > * the next instance. Thus, if we do not account that, we are >> > > > * stealing bandwidth from the system at each deadline miss! >> > > > */ >> > > > - if (dmiss) { >> > > > - dl_se->runtime = rorun ? dl_se->runtime : 0; >> > >> > If we didn't return 0 before, we are going to throttle (or replenish) >> > the entity, and you want runtime to be <=0. So, this is needed. >> > >> > > > - dl_se->runtime -= rq_clock(rq) - dl_se->deadline; >> > > > - } >> > >> > A little pessimism in some cases, due to the fact that we use both >> > rq_clock and rq_clock_task (for the budget). >> > >> > Thanks, >> > >> > - Juri >> > >> > > > + if (dmiss && !rorun) >> > > > + dl_se->runtime = dl_se->deadline - rq_clock(rq); >> > > > >> > > > return 1; >> > > > } >> > > > -- >> > > > 1.8.1.2 >> > > > >> > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/