From: Vincent Guittot <vincent.guittot@linaro.org> To: Mel Gorman <mgorman@techsingularity.net> Cc: LKML <linux-kernel@vger.kernel.org>, Aubrey Li <aubrey.li@linux.intel.com>, Barry Song <song.bao.hua@hisilicon.com>, Ingo Molnar <mingo@redhat.com>, Peter Ziljstra <peterz@infradead.org>, Juri Lelli <juri.lelli@redhat.com>, Valentin Schneider <valentin.schneider@arm.com>, Linux-ARM <linux-arm-kernel@lists.infradead.org> Subject: Re: [PATCH 3/4] sched/fair: Return an idle cpu if one is found after a failed search for an idle core Date: Mon, 7 Dec 2020 16:06:42 +0100 [thread overview] Message-ID: <CAKfTPtDYvOraCUjs94UCVSOjmJxxJhsF3t1ZNb_h+vSeOC0+VA@mail.gmail.com> (raw) In-Reply-To: <20201207091516.24683-4-mgorman@techsingularity.net> On Mon, 7 Dec 2020 at 10:15, Mel Gorman <mgorman@techsingularity.net> wrote: > > select_idle_core is called when SMT is active and there is likely a free > core available. It may find idle CPUs but this information is simply > discarded and the scan starts over again with select_idle_cpu. > > This patch caches information on idle CPUs found during the search for > a core and uses one if no core is found. This is a tradeoff. There may > be a slight impact when utilisation is low and an idle core can be > found quickly. It provides improvements as the number of busy CPUs > approaches 50% of the domain size when SMT is enabled. > > With tbench on a 2-socket CascadeLake machine, 80 logical CPUs, HT enabled > > 5.10.0-rc6 5.10.0-rc6 > schedstat idlecandidate > Hmean 1 500.06 ( 0.00%) 505.67 * 1.12%* > Hmean 2 975.90 ( 0.00%) 974.06 * -0.19%* > Hmean 4 1902.95 ( 0.00%) 1904.43 * 0.08%* > Hmean 8 3761.73 ( 0.00%) 3721.02 * -1.08%* > Hmean 16 6713.93 ( 0.00%) 6769.17 * 0.82%* > Hmean 32 10435.31 ( 0.00%) 10312.58 * -1.18%* > Hmean 64 12325.51 ( 0.00%) 13792.01 * 11.90%* > Hmean 128 21225.21 ( 0.00%) 20963.44 * -1.23%* > Hmean 256 20532.83 ( 0.00%) 20335.62 * -0.96%* > Hmean 320 20334.81 ( 0.00%) 20147.25 * -0.92%* > > Note that there is a significant corner case. As the SMT scan may be > terminated early, not all CPUs have been visited and select_idle_cpu() > is still called for a full scan. This case is handled in the next > patch. > > Signed-off-by: Mel Gorman <mgorman@techsingularity.net> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> > --- > kernel/sched/fair.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 01b38fc17bca..00c3b526a5bd 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6066,6 +6066,7 @@ void __update_idle_core(struct rq *rq) > */ > static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int target) > { > + int idle_candidate = -1; > struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask); > int core, cpu; > > @@ -6085,6 +6086,11 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int > idle = false; > break; > } > + > + if (idle_candidate == -1 && > + cpumask_test_cpu(cpu, p->cpus_ptr)) { > + idle_candidate = cpu; > + } > } > > if (idle) > @@ -6098,7 +6104,7 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int > */ > set_idle_cores(target, 0); > > - return -1; > + return idle_candidate; > } > > /* > -- > 2.26.2 >
WARNING: multiple messages have this Message-ID (diff)
From: Vincent Guittot <vincent.guittot@linaro.org> To: Mel Gorman <mgorman@techsingularity.net> Cc: Barry Song <song.bao.hua@hisilicon.com>, Juri Lelli <juri.lelli@redhat.com>, Peter Ziljstra <peterz@infradead.org>, Aubrey Li <aubrey.li@linux.intel.com>, LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@redhat.com>, Valentin Schneider <valentin.schneider@arm.com>, Linux-ARM <linux-arm-kernel@lists.infradead.org> Subject: Re: [PATCH 3/4] sched/fair: Return an idle cpu if one is found after a failed search for an idle core Date: Mon, 7 Dec 2020 16:06:42 +0100 [thread overview] Message-ID: <CAKfTPtDYvOraCUjs94UCVSOjmJxxJhsF3t1ZNb_h+vSeOC0+VA@mail.gmail.com> (raw) In-Reply-To: <20201207091516.24683-4-mgorman@techsingularity.net> On Mon, 7 Dec 2020 at 10:15, Mel Gorman <mgorman@techsingularity.net> wrote: > > select_idle_core is called when SMT is active and there is likely a free > core available. It may find idle CPUs but this information is simply > discarded and the scan starts over again with select_idle_cpu. > > This patch caches information on idle CPUs found during the search for > a core and uses one if no core is found. This is a tradeoff. There may > be a slight impact when utilisation is low and an idle core can be > found quickly. It provides improvements as the number of busy CPUs > approaches 50% of the domain size when SMT is enabled. > > With tbench on a 2-socket CascadeLake machine, 80 logical CPUs, HT enabled > > 5.10.0-rc6 5.10.0-rc6 > schedstat idlecandidate > Hmean 1 500.06 ( 0.00%) 505.67 * 1.12%* > Hmean 2 975.90 ( 0.00%) 974.06 * -0.19%* > Hmean 4 1902.95 ( 0.00%) 1904.43 * 0.08%* > Hmean 8 3761.73 ( 0.00%) 3721.02 * -1.08%* > Hmean 16 6713.93 ( 0.00%) 6769.17 * 0.82%* > Hmean 32 10435.31 ( 0.00%) 10312.58 * -1.18%* > Hmean 64 12325.51 ( 0.00%) 13792.01 * 11.90%* > Hmean 128 21225.21 ( 0.00%) 20963.44 * -1.23%* > Hmean 256 20532.83 ( 0.00%) 20335.62 * -0.96%* > Hmean 320 20334.81 ( 0.00%) 20147.25 * -0.92%* > > Note that there is a significant corner case. As the SMT scan may be > terminated early, not all CPUs have been visited and select_idle_cpu() > is still called for a full scan. This case is handled in the next > patch. > > Signed-off-by: Mel Gorman <mgorman@techsingularity.net> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> > --- > kernel/sched/fair.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 01b38fc17bca..00c3b526a5bd 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6066,6 +6066,7 @@ void __update_idle_core(struct rq *rq) > */ > static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int target) > { > + int idle_candidate = -1; > struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask); > int core, cpu; > > @@ -6085,6 +6086,11 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int > idle = false; > break; > } > + > + if (idle_candidate == -1 && > + cpumask_test_cpu(cpu, p->cpus_ptr)) { > + idle_candidate = cpu; > + } > } > > if (idle) > @@ -6098,7 +6104,7 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int > */ > set_idle_cores(target, 0); > > - return -1; > + return idle_candidate; > } > > /* > -- > 2.26.2 > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-12-07 15:07 UTC|newest] Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-12-07 9:15 [RFC PATCH 0/4] Reduce worst-case scanning of runqueues in select_idle_sibling Mel Gorman 2020-12-07 9:15 ` Mel Gorman 2020-12-07 9:15 ` [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU Mel Gorman 2020-12-07 9:15 ` Mel Gorman 2020-12-07 15:05 ` Vincent Guittot 2020-12-07 15:05 ` Vincent Guittot 2020-12-08 10:07 ` Dietmar Eggemann 2020-12-08 10:07 ` Dietmar Eggemann 2020-12-08 10:59 ` Mel Gorman 2020-12-08 10:59 ` Mel Gorman 2020-12-08 13:24 ` Vincent Guittot 2020-12-08 13:24 ` Vincent Guittot 2020-12-08 13:36 ` Mel Gorman 2020-12-08 13:36 ` Mel Gorman 2020-12-08 13:43 ` Vincent Guittot 2020-12-08 13:43 ` Vincent Guittot 2020-12-08 13:53 ` Mel Gorman 2020-12-08 13:53 ` Mel Gorman 2020-12-08 14:47 ` Vincent Guittot 2020-12-08 14:47 ` Vincent Guittot 2020-12-08 15:12 ` Mel Gorman 2020-12-08 15:12 ` Mel Gorman 2020-12-08 15:19 ` Vincent Guittot 2020-12-08 15:19 ` Vincent Guittot 2020-12-07 9:15 ` [PATCH 2/4] sched/fair: Do not replace recent_used_cpu with the new target Mel Gorman 2020-12-07 9:15 ` Mel Gorman 2020-12-08 9:57 ` Dietmar Eggemann 2020-12-08 9:57 ` Dietmar Eggemann 2020-12-08 11:02 ` Mel Gorman 2020-12-08 11:02 ` Mel Gorman 2020-12-07 9:15 ` [PATCH 3/4] sched/fair: Return an idle cpu if one is found after a failed search for an idle core Mel Gorman 2020-12-07 9:15 ` Mel Gorman 2020-12-07 15:06 ` Vincent Guittot [this message] 2020-12-07 15:06 ` Vincent Guittot 2020-12-07 9:15 ` [PATCH 4/4] sched/fair: Avoid revisiting CPUs multiple times during select_idle_sibling Mel Gorman 2020-12-07 9:15 ` Mel Gorman 2020-12-07 15:04 ` [RFC PATCH 0/4] Reduce worst-case scanning of runqueues in select_idle_sibling Vincent Guittot 2020-12-07 15:04 ` Vincent Guittot 2020-12-07 15:42 ` Mel Gorman 2020-12-07 15:42 ` Mel Gorman 2020-12-08 2:06 ` Li, Aubrey 2020-12-08 2:06 ` Li, Aubrey
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