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[141.239.159.203]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7065107b62bsm7011138b3a.16.2024.06.24.16.59.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Jun 2024 16:59:03 -0700 (PDT) Sender: Tejun Heo Date: Mon, 24 Jun 2024 13:59:02 -1000 From: Tejun Heo To: Peter Zijlstra Cc: torvalds@linux-foundation.org, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@kernel.org, joshdon@google.com, brho@google.com, pjt@google.com, derkling@google.com, haoluo@google.com, dvernet@meta.com, dschatzberg@meta.com, dskarlat@cs.cmu.edu, riel@surriel.com, changwoo@igalia.com, himadrics@inria.fr, memxor@gmail.com, andrea.righi@canonical.com, joel@joelfernandes.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH 04/39] sched: Add sched_class->reweight_task() Message-ID: References: <20240501151312.635565-1-tj@kernel.org> <20240501151312.635565-5-tj@kernel.org> <20240624102331.GI31592@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: <20240624102331.GI31592@noisy.programming.kicks-ass.net> Hello, Peter. On Mon, Jun 24, 2024 at 12:23:31PM +0200, Peter Zijlstra wrote: > This reminds me, I think we have a bug here... > > https://lkml.kernel.org/r/20240422094157.GA34453@noisy.programming.kicks-ass.net > > I *think* we want something like the below, hmm? > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 0935f9d4bb7b..32a40d85c0b1 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -1328,15 +1328,15 @@ int tg_nop(struct task_group *tg, void *data) > void set_load_weight(struct task_struct *p, bool update_load) > { > int prio = p->static_prio - MAX_RT_PRIO; > - struct load_weight *load = &p->se.load; > + unsigned long weight; > + u32 inv_weight; > > - /* > - * SCHED_IDLE tasks get minimal weight: > - */ > if (task_has_idle_policy(p)) { > - load->weight = scale_load(WEIGHT_IDLEPRIO); > - load->inv_weight = WMULT_IDLEPRIO; > - return; > + weight = scale_load(WEIGHT_IDLEPRIO); > + inv_weight = WMULT_IDLEPRIO; > + } else { > + weight = scale_load(sched_prio_to_weight[prio]); > + inv_weight = sched_prio_to_wmult[prio]; Hmmm... sorry but I'm a bit confused again. Isn't the code doing the same thing before and after? Before, if @p is SCHED_IDLE, @p->se.load is set to idle values and the function returns. If @update_load && fair, calls reweight_task(). Otherwise, update @p->se.load is updated according to @prio. After the patch, @weight and @inv_weight calcuations are moved to set_load_weight() but it ends up with the same result for all three cases. Were you trying to say that if the idle policy were to implement ->reweight_task(), it wouldn't be called? Thanks. -- tejun