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Thu, 01 Oct 2026 08:26:02 -0700 (PDT) Received: from jlelli-thinkpadt14gen4.remote.csb ([176.206.14.6]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48b0690e721sm7077992f8f.20.2026.10.01.08.26.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Oct 2026 08:26:01 -0700 (PDT) Date: Thu, 1 Oct 2026 17:25:59 +0200 From: Juri Lelli To: Peter Zijlstra 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=?= , ionut.nechita@windriver.com Subject: Re: [PATCH v2] sched/deadline: Make dl-server nohz full aware Message-ID: References: <20260513-upstream-fix-dlserver-nohzfull-b4-v2-1-d3e9cbe5c845@redhat.com> <20261001142735.GT2009045@noisy.programming.kicks-ass.net> <20261001143314.GK4121620@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: <20261001143314.GK4121620@noisy.programming.kicks-ass.net> On 01/10/26 16:33, Peter Zijlstra wrote: > On Thu, Oct 01, 2026 at 04:27:36PM +0200, Peter Zijlstra wrote: > > > > bool sched_can_stop_tick(struct rq *rq) > > > { > > > /* Deadline tasks, even if single, need the tick */ > > > if (rq->dl.dl_nr_running) > > > return false; > > > > > > /* > > > + * If there are RT tasks, we may need the tick (for >1 RR tasks), > > > + * but we must also service lower-priority CFS/SCX tasks via dl-servers. > > > */ > > > + if (rq->rt.rt_nr_running) { > > > + bool cfs_or_scx_queued = false; > > > + > > > + if (rq->cfs.h_nr_queued) { > > > + dl_server_start(&rq->fair_server); > > > + cfs_or_scx_queued = true; > > > + } > > > +#ifdef CONFIG_SCHED_CLASS_EXT > > > + if (rq->scx.nr_running) { > > > + dl_server_start(&rq->ext_server); > > > + cfs_or_scx_queued = true; > > > + } > > > +#endif > > > + if (cfs_or_scx_queued) > > > return false; > > What the purpose of this boolean, both true assignments above can simply > be return false, no? But we won't start the ext_server, even if EXT tasks are present, if we return false in case CFS tasks are present. > > > > > > > + /* > > > + * Only RT tasks, no CFS/SCX. Stop servers to prevent spurious > > No DL either, you've filtered those out above. Right. > > > > + * wakeups. Tick can stop for single RR or any FIFO, but must > > > + * run for multiple RR (round-robin behavior). > > > + */ > > > + dl_servers_stop_all(rq); > > > + if (rq->rt.rr_nr_running > 1) > > > + return false; > > > return true; > > > + } >