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Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1xCZRs-0000000GWp6-0Pvv; Fri, 02 Oct 2026 09:21:00 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 03322300390; Fri, 02 Oct 2026 11:20:59 +0200 (CEST) Date: Fri, 2 Oct 2026 11:20:58 +0200 From: Peter Zijlstra To: Juri Lelli Cc: Ingo Molnar , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Andrea Righi , Frederic Weisbecker , linux-kernel@vger.kernel.org, David Haufe , Cao Ruichuang , Furkan =?utf-8?B?w4dhbMSxxZ9rYW4=?= Subject: Re: [PATCH v2] sched/deadline: Make dl-server nohz full aware Message-ID: <20261002092058.GA409038@noisy.programming.kicks-ass.net> References: <20260513-upstream-fix-dlserver-nohzfull-b4-v2-1-d3e9cbe5c845@redhat.com> <20261001142735.GT2009045@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261001142735.GT2009045@noisy.programming.kicks-ass.net> On Thu, Oct 01, 2026 at 04:27:36PM +0200, Peter Zijlstra wrote: > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > index 0663c00c41c0..5388bde93410 100644 > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -401,6 +401,7 @@ static void __dl_clear_params(struct sched_dl_entity *dl_se); > */ > static void task_non_contending(struct sched_dl_entity *dl_se, bool dl_task) > { > + enum hrtimer_mode mode = HRTIMER_MODE_REL_HARD; > struct hrtimer *timer = &dl_se->inactive_timer; > struct rq *rq = rq_of_dl_se(dl_se); > struct dl_rq *dl_rq = &rq->dl; > @@ -459,8 +460,10 @@ static void task_non_contending(struct sched_dl_entity *dl_se, bool dl_task) > dl_se->dl_non_contending = 1; > if (!dl_server(dl_se)) > get_task_struct(dl_task_of(dl_se)); > + else > + mode |= HRTIMER_MODE_PINNED; > > - hrtimer_start(timer, ns_to_ktime(zerolag_time), HRTIMER_MODE_REL_HARD); > + hrtimer_start(timer, ns_to_ktime(zerolag_time), mode); > } > > static void task_contending(struct sched_dl_entity *dl_se, int flags) > @@ -1061,6 +1064,7 @@ static inline u64 dl_next_period(struct sched_dl_entity *dl_se) > */ > static int start_dl_timer(struct sched_dl_entity *dl_se) > { > + enum hrtimer_mode mode = HRTIMER_MODE_ABS_HARD; > struct hrtimer *timer = &dl_se->dl_timer; > struct dl_rq *dl_rq = dl_rq_of_se(dl_se); > struct rq *rq = rq_of_dl_rq(dl_rq); > @@ -1112,7 +1116,9 @@ static int start_dl_timer(struct sched_dl_entity *dl_se) > if (!hrtimer_is_queued(timer)) { > if (!dl_server(dl_se)) > get_task_struct(dl_task_of(dl_se)); > - hrtimer_start(timer, act, HRTIMER_MODE_ABS_HARD); > + else > + mode |= HRTIMER_MODE_PINNED; > + hrtimer_start(timer, act, mode); > } > > return 1; Bah, this would require something like: hrtime_start_on(timer, act, mode, rq->cpu); which we don't currently have. The problem is that on remote enqueue, we can start the dl-server remotely, and it then being pinned, means its on the 'wrong' CPU. Doing remote hrtimer_start isn't entirely trivial either. So scrap this for now :-(