Messages in this thread | | | Date | Thu, 6 Jun 2019 09:12:13 +0100 | From | Quentin Perret <> | Subject | Re: [PATCH] sched/fair: Introduce fits_capacity() |
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On Thursday 06 Jun 2019 at 08:22:04 (+0530), Viresh Kumar wrote: > On 05-06-19, 10:16, Quentin Perret wrote: > > Hi Viresh, > > > > On Tuesday 04 Jun 2019 at 12:31:52 (+0530), Viresh Kumar wrote: > > > The same formula to check utilization against capacity (after > > > considering capacity_margin) is already used at 5 different locations. > > > > > > This patch creates a new macro, fits_capacity(), which can be used from > > > all these locations without exposing the details of it and hence > > > simplify code. > > > > > > All the 5 code locations are updated as well to use it.. > > > > > > Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> > > > --- > > > kernel/sched/fair.c | 14 +++++++------- > > > 1 file changed, 7 insertions(+), 7 deletions(-) > > > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > > index 7f8d477f90fe..db3a218b7928 100644 > > > --- a/kernel/sched/fair.c > > > +++ b/kernel/sched/fair.c > > > @@ -102,6 +102,8 @@ int __weak arch_asym_cpu_priority(int cpu) > > > * (default: ~20%) > > > */ > > > static unsigned int capacity_margin = 1280; > > > + > > > +#define fits_capacity(cap, max) ((cap) * capacity_margin < (max) * 1024) > > > #endif > > > > > > #ifdef CONFIG_CFS_BANDWIDTH > > > @@ -3727,7 +3729,7 @@ util_est_dequeue(struct cfs_rq *cfs_rq, struct task_struct *p, bool task_sleep) > > > > > > static inline int task_fits_capacity(struct task_struct *p, long capacity) > > > { > > > - return capacity * 1024 > task_util_est(p) * capacity_margin; > > > + return fits_capacity(task_util_est(p), capacity); > > > } > > > > > > static inline void update_misfit_status(struct task_struct *p, struct rq *rq) > > > @@ -5143,7 +5145,7 @@ static inline unsigned long cpu_util(int cpu); > > > > > > static inline bool cpu_overutilized(int cpu) > > > { > > > - return (capacity_of(cpu) * 1024) < (cpu_util(cpu) * capacity_margin); > > > + return !fits_capacity(cpu_util(cpu), capacity_of(cpu)); > > > > This ... > > > > > } > > > > > > static inline void update_overutilized_status(struct rq *rq) > > > @@ -6304,7 +6306,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) > > > /* Skip CPUs that will be overutilized. */ > > > util = cpu_util_next(cpu, p, cpu); > > > cpu_cap = capacity_of(cpu); > > > - if (cpu_cap * 1024 < util * capacity_margin) > > > + if (!fits_capacity(util, cpu_cap)) > > > > ... and this isn't _strictly_ equivalent to the existing code but I > > guess we can live with the difference :-) > > Yes, I missed the == part it seems. Good catch. Though as you said, > maybe we don't need to take that into account and can live with the > new macro :) > > > > > > continue; > > > > > > /* Always use prev_cpu as a candidate. */ > > > @@ -7853,8 +7855,7 @@ group_is_overloaded(struct lb_env *env, struct sg_lb_stats *sgs) > > > static inline bool > > > group_smaller_min_cpu_capacity(struct sched_group *sg, struct sched_group *ref) > > > { > > > - return sg->sgc->min_capacity * capacity_margin < > > > - ref->sgc->min_capacity * 1024; > > > + return fits_capacity(sg->sgc->min_capacity, ref->sgc->min_capacity); > > > } > > > > > > /* > > > @@ -7864,8 +7865,7 @@ group_smaller_min_cpu_capacity(struct sched_group *sg, struct sched_group *ref) > > > static inline bool > > > group_smaller_max_cpu_capacity(struct sched_group *sg, struct sched_group *ref) > > > { > > > - return sg->sgc->max_capacity * capacity_margin < > > > - ref->sgc->max_capacity * 1024; > > > + return fits_capacity(sg->sgc->max_capacity, ref->sgc->max_capacity); > > > } > > > > > > static inline enum > > > -- > > > 2.21.0.rc0.269.g1a574e7a288b > > > > > > > Also, since we're talking about making the capacity_margin code more > > consistent, one small thing I had in mind: we have a capacity margin > > in sugov too, which happens to be 1.25 has well (see map_util_freq()). > > Conceptually, capacity_margin in fair.c and the sugov margin are both > > about answering: "do I have enough CPU capacity to serve X of util, or > > do I need more ?" > > > > So perhaps we should factorize the capacity_margin code some more to use > > it in both places in a consistent way ? This could be done in a separate > > patch, though. > > Hmm, even if the values are same currently I am not sure if we want > the same for ever.
Right, that's a good point. It is cheaper to raise the freq on a CPU than to migrate a task, so perhaps there could be a case for different thresholds ...
> I will write a patch for it though, if Peter/Rafael > feel the same as you.
Sounds good, thanks ! Quentin
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