| Message ID | 20201208153501.1467-2-mgorman@techsingularity.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Reduce scanning of runqueues in select_idle_sibling | expand |
On Tue, 8 Dec 2020 at 16:35, Mel Gorman <mgorman@techsingularity.net> wrote: > > SIS_AVG_CPU was introduced as a means of avoiding a search when the > average search cost indicated that the search would likely fail. It > was a blunt instrument and disabled by 4c77b18cf8b7 ("sched/fair: Make > select_idle_cpu() more aggressive") and later replaced with a proportional > search depth by 1ad3aaf3fcd2 ("sched/core: Implement new approach to > scale select_idle_cpu()"). > > While there are corner cases where SIS_AVG_CPU is better, it has now been > disabled for almost three years. As the intent of SIS_PROP is to reduce > the time complexity of select_idle_cpu(), lets drop SIS_AVG_CPU and focus > on SIS_PROP as a throttling mechanism. > > Signed-off-by: Mel Gorman <mgorman@techsingularity.net> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> > --- > kernel/sched/fair.c | 20 +++++++++----------- > kernel/sched/features.h | 1 - > 2 files changed, 9 insertions(+), 12 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 98075f9ea9a8..ac7b34e7372b 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6145,7 +6145,6 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t > { > struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask); > struct sched_domain *this_sd; > - u64 avg_cost, avg_idle; > u64 time; > int this = smp_processor_id(); > int cpu, nr = INT_MAX; > @@ -6154,18 +6153,17 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t > if (!this_sd) > return -1; > > - /* > - * Due to large variance we need a large fuzz factor; hackbench in > - * particularly is sensitive here. > - */ > - avg_idle = this_rq()->avg_idle / 512; > - avg_cost = this_sd->avg_scan_cost + 1; > + if (sched_feat(SIS_PROP)) { > + u64 avg_cost, avg_idle, span_avg; > > - if (sched_feat(SIS_AVG_CPU) && avg_idle < avg_cost) > - return -1; > + /* > + * Due to large variance we need a large fuzz factor; > + * hackbench in particularly is sensitive here. > + */ > + avg_idle = this_rq()->avg_idle / 512; > + avg_cost = this_sd->avg_scan_cost + 1; > > - if (sched_feat(SIS_PROP)) { > - u64 span_avg = sd->span_weight * avg_idle; > + span_avg = sd->span_weight * avg_idle; > if (span_avg > 4*avg_cost) > nr = div_u64(span_avg, avg_cost); > else > diff --git a/kernel/sched/features.h b/kernel/sched/features.h > index 68d369cba9e4..e875eabb6600 100644 > --- a/kernel/sched/features.h > +++ b/kernel/sched/features.h > @@ -54,7 +54,6 @@ SCHED_FEAT(TTWU_QUEUE, true) > /* > * When doing wakeups, attempt to limit superfluous scans of the LLC domain. > */ > -SCHED_FEAT(SIS_AVG_CPU, false) > SCHED_FEAT(SIS_PROP, true) > > /* > -- > 2.26.2 >
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 98075f9ea9a8..ac7b34e7372b 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6145,7 +6145,6 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t { struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask); struct sched_domain *this_sd; - u64 avg_cost, avg_idle; u64 time; int this = smp_processor_id(); int cpu, nr = INT_MAX; @@ -6154,18 +6153,17 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t if (!this_sd) return -1; - /* - * Due to large variance we need a large fuzz factor; hackbench in - * particularly is sensitive here. - */ - avg_idle = this_rq()->avg_idle / 512; - avg_cost = this_sd->avg_scan_cost + 1; + if (sched_feat(SIS_PROP)) { + u64 avg_cost, avg_idle, span_avg; - if (sched_feat(SIS_AVG_CPU) && avg_idle < avg_cost) - return -1; + /* + * Due to large variance we need a large fuzz factor; + * hackbench in particularly is sensitive here. + */ + avg_idle = this_rq()->avg_idle / 512; + avg_cost = this_sd->avg_scan_cost + 1; - if (sched_feat(SIS_PROP)) { - u64 span_avg = sd->span_weight * avg_idle; + span_avg = sd->span_weight * avg_idle; if (span_avg > 4*avg_cost) nr = div_u64(span_avg, avg_cost); else diff --git a/kernel/sched/features.h b/kernel/sched/features.h index 68d369cba9e4..e875eabb6600 100644 --- a/kernel/sched/features.h +++ b/kernel/sched/features.h @@ -54,7 +54,6 @@ SCHED_FEAT(TTWU_QUEUE, true) /* * When doing wakeups, attempt to limit superfluous scans of the LLC domain. */ -SCHED_FEAT(SIS_AVG_CPU, false) SCHED_FEAT(SIS_PROP, true) /*
SIS_AVG_CPU was introduced as a means of avoiding a search when the average search cost indicated that the search would likely fail. It was a blunt instrument and disabled by 4c77b18cf8b7 ("sched/fair: Make select_idle_cpu() more aggressive") and later replaced with a proportional search depth by 1ad3aaf3fcd2 ("sched/core: Implement new approach to scale select_idle_cpu()"). While there are corner cases where SIS_AVG_CPU is better, it has now been disabled for almost three years. As the intent of SIS_PROP is to reduce the time complexity of select_idle_cpu(), lets drop SIS_AVG_CPU and focus on SIS_PROP as a throttling mechanism. Signed-off-by: Mel Gorman <mgorman@techsingularity.net> --- kernel/sched/fair.c | 20 +++++++++----------- kernel/sched/features.h | 1 - 2 files changed, 9 insertions(+), 12 deletions(-)