| Message ID | 1415033687-23294-6-git-send-email-vincent.guittot@linaro.org |
|---|---|
| State | New |
| Headers | show |
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 . > > 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 > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
On 26 November 2014 at 06:18, Wanpeng Li <kernellwp@gmail.com> wrote: > 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"? No, Both are useful. sched_avg_period is useful to keep the value more stable across the time. Without sched_avg_period, it will be too much reactive ( especially at the beg of a period ). > > 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 >>> >>> > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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
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) 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(-)