Messages in this thread Patch in this message | | | Date | Mon, 20 Jul 2015 17:37:20 -0700 | From | Sai Gurrappadi <> | Subject | Re: [RFCv5 PATCH 31/46] sched: Consider spare cpu capacity at task wake-up |
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Hi Morten,
On 07/07/2015 11:24 AM, Morten Rasmussen wrote: > In mainline find_idlest_group() selects the wake-up target group purely > based on group load which leads to suboptimal choices in low load > scenarios. An idle group with reduced capacity (due to RT tasks or > different cpu type) isn't necessarily a better target than a lightly > loaded group with higher capacity. > > The patch adds spare capacity as an additional group selection > parameter. The target group is now selected based on the following > criteria listed by highest priority first: > > 1. If energy-aware scheduling is enabled the group with the lowest > capacity containing a cpu with enough spare capacity to accommodate the > task (with a bit to spare) is selected if such exists. > > 2. Return the group with the cpu with most spare capacity and this > capacity is significant if such group exists. Significant spare capacity > is currently at least 20% to spare. > > 3. Return the group with the lowest load, unless it is the local group > in which case NULL is returned and the search is continued at the next > (lower) level. > > cc: Ingo Molnar <mingo@redhat.com> > cc: Peter Zijlstra <peterz@infradead.org> > > Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com> > --- > kernel/sched/fair.c | 18 ++++++++++++++++-- > 1 file changed, 16 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index b0294f0..0f7dbda4 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -5247,9 +5247,10 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, > int this_cpu, int sd_flag) > { > struct sched_group *idlest = NULL, *group = sd->groups; > - struct sched_group *fit_group = NULL; > + struct sched_group *fit_group = NULL, *spare_group = NULL; > unsigned long min_load = ULONG_MAX, this_load = 0; > unsigned long fit_capacity = ULONG_MAX; > + unsigned long max_spare_capacity = capacity_margin - SCHED_LOAD_SCALE; > int load_idx = sd->forkexec_idx; > int imbalance = 100 + (sd->imbalance_pct-100)/2; > > @@ -5257,7 +5258,7 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, > load_idx = sd->wake_idx; > > do { > - unsigned long load, avg_load; > + unsigned long load, avg_load, spare_capacity; > int local_group; > int i; > > @@ -5290,6 +5291,16 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, > fit_capacity = capacity_of(i); > fit_group = group; > } > + > + /* > + * Look for group which has most spare capacity on a > + * single cpu. > + */ > + spare_capacity = capacity_of(i) - get_cpu_usage(i); > + if (spare_capacity > max_spare_capacity) { > + max_spare_capacity = spare_capacity; > + spare_group = group; > + }
Another minor buglet: get_cpu_usage(i) here could be > capacity_of(i) because usage is bounded by capacity_orig_of(i). Should it be bounded by capacity_of() instead?
> } > > /* Adjust by relative CPU capacity of the group */ > @@ -5306,6 +5317,9 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, > if (fit_group) > return fit_group; > > + if (spare_group) > + return spare_group; > + > if (!idlest || 100*this_load < imbalance*min_load) > return NULL; > return idlest; >
Thanks, -Sai
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