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[73.202.176.14]) by smtp.gmail.com with ESMTPSA id h11-20020a63210b000000b005dcc8a3b26esm1861016pgh.16.2024.04.05.14.12.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 05 Apr 2024 14:12:01 -0700 (PDT) From: Benjamin Segall To: Peter Zijlstra Cc: mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, linux-kernel@vger.kernel.org, kprateek.nayak@amd.com, wuyun.abel@bytedance.com, tglx@linutronix.de, efault@gmx.de Subject: Re: [RFC][PATCH 03/10] sched/fair: Cleanup pick_task_fair() vs throttle In-Reply-To: <20240405110010.024746026@infradead.org> (Peter Zijlstra's message of "Fri, 05 Apr 2024 12:27:57 +0200") References: <20240405102754.435410987@infradead.org> <20240405110010.024746026@infradead.org> Date: Fri, 05 Apr 2024 14:11:57 -0700 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Peter Zijlstra writes: > Per 54d27365cae8 ("sched/fair: Prevent throttling in early > pick_next_task_fair()") the reason check_cfs_rq_runtime() is under the > 'if (curr)' check is to ensure the (downward) traversal does not > result in an empty cfs_rq. > > But then the pick_task_fair() 'copy' of all this made it restart the > traversal anyway, so that seems to solve the issue too. Yeah, putting the check_cfs_rq_runtime inside of that condition was specific to the exact pnt_fair code, and the specific places that nr_running was and was not checked. pick_task_fair doesn't care about any of that, and if instead put_prev manages to throttle the picked task, we can still successfully switch to it for a moment. Reviewed-by: Ben Segall > > Signed-off-by: Peter Zijlstra (Intel) > --- > kernel/sched/fair.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -8435,11 +8435,11 @@ static struct task_struct *pick_task_fai > update_curr(cfs_rq); > else > curr = NULL; > - > - if (unlikely(check_cfs_rq_runtime(cfs_rq))) > - goto again; > } > > + if (unlikely(check_cfs_rq_runtime(cfs_rq))) > + goto again; > + > se = pick_next_entity(cfs_rq); > cfs_rq = group_cfs_rq(se); > } while (cfs_rq);