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[61.68.227.232]) by smtp.gmail.com with ESMTPSA id d2sm9797254pjj.37.2020.11.22.02.35.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 22 Nov 2020 02:35:33 -0800 (PST) Date: Sun, 22 Nov 2020 21:35:29 +1100 From: Balbir Singh To: "Joel Fernandes (Google)" Cc: Nishanth Aravamudan , Julien Desfossez , Peter Zijlstra , Tim Chen , Vineeth Pillai , Aaron Lu , Aubrey Li , tglx@linutronix.de, linux-kernel@vger.kernel.org, mingo@kernel.org, torvalds@linux-foundation.org, fweisbec@gmail.com, keescook@chromium.org, kerrnel@google.com, Phil Auld , Valentin Schneider , Mel Gorman , Pawan Gupta , Paolo Bonzini , vineeth@bitbyteword.org, Chen Yu , Christian Brauner , Agata Gruza , Antonio Gomez Iglesias , graf@amazon.com, konrad.wilk@oracle.com, dfaggioli@suse.com, pjt@google.com, rostedt@goodmis.org, derkling@google.com, benbjiang@tencent.com, Alexandre Chartre , James.Bottomley@hansenpartnership.com, OWeisse@umich.edu, Dhaval Giani , Junaid Shahid , jsbarnes@google.com, chris.hyser@oracle.com, Ben Segall , Josh Don , Hao Luo , Tom Lendacky , Aubrey Li , "Paul E. McKenney" , Tim Chen Subject: Re: [PATCH -tip 08/32] sched/fair: Fix forced idle sibling starvation corner case Message-ID: <20201122103529.GC110669@balbir-desktop> References: <20201117232003.3580179-1-joel@joelfernandes.org> <20201117232003.3580179-9-joel@joelfernandes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201117232003.3580179-9-joel@joelfernandes.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 17, 2020 at 06:19:38PM -0500, Joel Fernandes (Google) wrote: > From: Vineeth Pillai > > If there is only one long running local task and the sibling is > forced idle, it might not get a chance to run until a schedule > event happens on any cpu in the core. > > So we check for this condition during a tick to see if a sibling > is starved and then give it a chance to schedule. > > Tested-by: Julien Desfossez > Reviewed-by: Joel Fernandes (Google) > Signed-off-by: Vineeth Pillai > Signed-off-by: Julien Desfossez > Signed-off-by: Joel Fernandes (Google) > --- > kernel/sched/core.c | 15 ++++++++------- > kernel/sched/fair.c | 40 ++++++++++++++++++++++++++++++++++++++++ > kernel/sched/sched.h | 2 +- > 3 files changed, 49 insertions(+), 8 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 1bd0b0bbb040..52d0e83072a4 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -5206,16 +5206,15 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) > > /* reset state */ > rq->core->core_cookie = 0UL; > + if (rq->core->core_forceidle) { > + need_sync = true; > + rq->core->core_forceidle = false; > + } > for_each_cpu(i, smt_mask) { > struct rq *rq_i = cpu_rq(i); > > rq_i->core_pick = NULL; > > - if (rq_i->core_forceidle) { > - need_sync = true; > - rq_i->core_forceidle = false; > - } > - > if (i != cpu) > update_rq_clock(rq_i); > } > @@ -5335,8 +5334,10 @@ next_class:; > if (!rq_i->core_pick) > continue; > > - if (is_task_rq_idle(rq_i->core_pick) && rq_i->nr_running) > - rq_i->core_forceidle = true; > + if (is_task_rq_idle(rq_i->core_pick) && rq_i->nr_running && > + !rq_i->core->core_forceidle) { > + rq_i->core->core_forceidle = true; > + } > > if (i == cpu) { > rq_i->core_pick = NULL; > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index f53681cd263e..42965c4fd71f 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -10692,6 +10692,44 @@ static void rq_offline_fair(struct rq *rq) > > #endif /* CONFIG_SMP */ > > +#ifdef CONFIG_SCHED_CORE > +static inline bool > +__entity_slice_used(struct sched_entity *se, int min_nr_tasks) > +{ > + u64 slice = sched_slice(cfs_rq_of(se), se); I wonder if the definition of sched_slice() should be revisited for core scheduling? Should we use sched_slice = sched_slice / cpumask_weight(smt_mask)? Would that resolve the issue your seeing? Effectively we need to answer if two sched core siblings should be treated as executing one large slice? Balbir Singh.