Messages in this thread | | | Date | Wed, 26 Nov 2014 13:18:05 +0800 | From | Wanpeng Li <> | Subject | Re: [PATCH v9 05/10] sched: make scale_rt invariant with frequency |
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Hi Vincent, On 11/25/14, 9:52 PM, Vincent Guittot wrote: > On 25 November 2014 at 03:24, Wanpeng Li <kernellwp@gmail.com> wrote: >> Hi Vincent, >> On 11/4/14, 12:54 AM, Vincent Guittot wrote: >>> The average running time of RT tasks is used to estimate the remaining >>> compute >>> capacity for CFS tasks. This remaining capacity is the original capacity >>> scaled >>> down by a factor (aka scale_rt_capacity). This estimation of available >>> capacity >>> must also be invariant with frequency scaling. >>> >>> A frequency scaling factor is applied on the running time of the RT tasks >>> for >>> computing scale_rt_capacity. >>> >>> In sched_rt_avg_update, we scale the RT execution time like below: >>> rq->rt_avg += rt_delta * arch_scale_freq_capacity() >> >>> SCHED_CAPACITY_SHIFT >>> >>> Then, scale_rt_capacity can be summarized by: >>> scale_rt_capacity = SCHED_CAPACITY_SCALE - >>> ((rq->rt_avg << SCHED_CAPACITY_SHIFT) / period) >> >> The 'period' aka 'total' in the scale_rt_capacity(), why it is >> sched_avg_period() + delta instead of sched_avg_period()? > The default value of sched_avg_period is 1sec which is "long" so we > take into account the time consumed by RT tasks in the ongoing period > .
Do you mean 'sched_avg_period() + delta' should be replaced by 'delta' since sched_avg_period() is "long"?
Regards, Wanpeng Li
> >> Regards, >> Wanpeng Li >> >> >>> We can optimize by removing right and left shift in the computation of >>> rq->rt_avg >>> and scale_rt_capacity >>> >>> The call to arch_scale_frequency_capacity in the rt scheduling path might >>> be >>> a concern for RT folks because I'm not sure whether we can rely on >>> arch_scale_freq_capacity to be short and efficient ? >>> >>> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> >>> --- >>> kernel/sched/fair.c | 17 +++++------------ >>> kernel/sched/sched.h | 4 +++- >>> 2 files changed, 8 insertions(+), 13 deletions(-) >>> >>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >>> index a5039da..b37c27b 100644 >>> --- a/kernel/sched/fair.c >>> +++ b/kernel/sched/fair.c >>> @@ -5785,7 +5785,7 @@ unsigned long __weak arch_scale_cpu_capacity(struct >>> sched_domain *sd, int cpu) >>> static unsigned long scale_rt_capacity(int cpu) >>> { >>> struct rq *rq = cpu_rq(cpu); >>> - u64 total, available, age_stamp, avg; >>> + u64 total, used, age_stamp, avg; >>> s64 delta; >>> /* >>> @@ -5801,19 +5801,12 @@ static unsigned long scale_rt_capacity(int cpu) >>> total = sched_avg_period() + delta; >>> - if (unlikely(total < avg)) { >>> - /* Ensures that capacity won't end up being negative */ >>> - available = 0; >>> - } else { >>> - available = total - avg; >>> - } >>> + used = div_u64(avg, total); >>> - if (unlikely((s64)total < SCHED_CAPACITY_SCALE)) >>> - total = SCHED_CAPACITY_SCALE; >>> + if (likely(used < SCHED_CAPACITY_SCALE)) >>> + return SCHED_CAPACITY_SCALE - used; >>> - total >>= SCHED_CAPACITY_SHIFT; >>> - >>> - return div_u64(available, total); >>> + return 1; >>> } >>> static void update_cpu_capacity(struct sched_domain *sd, int cpu) >>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h >>> index c34bd11..fc5b152 100644 >>> --- a/kernel/sched/sched.h >>> +++ b/kernel/sched/sched.h >>> @@ -1312,9 +1312,11 @@ static inline int hrtick_enabled(struct rq *rq) >>> #ifdef CONFIG_SMP >>> extern void sched_avg_update(struct rq *rq); >>> +extern unsigned long arch_scale_freq_capacity(struct sched_domain *sd, >>> int cpu); >>> + >>> static inline void sched_rt_avg_update(struct rq *rq, u64 rt_delta) >>> { >>> - rq->rt_avg += rt_delta; >>> + rq->rt_avg += rt_delta * arch_scale_freq_capacity(NULL, >>> cpu_of(rq)); >>> sched_avg_update(rq); >>> } >>> #else >>
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