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Re: [PATCH v2 07/13] sched/fair: Let asymmetric cpu configurations balance at wake-up

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  Re: [PATCH v2 07/13] sched/fair: Let asymmetric cpu configurations  balance at wake-up Vincent Guittot <vincent.guittot@linaro.org> - 2016-07-13 15:00 +0200
    Re: [PATCH v2 07/13] sched/fair: Let asymmetric cpu configurations  balance at wake-up Morten Rasmussen <morten.rasmussen@arm.com> - 2016-07-13 18:20 +0200
      Re: [PATCH v2 07/13] sched/fair: Let asymmetric cpu configurations  balance at wake-up Vincent Guittot <vincent.guittot@linaro.org> - 2016-07-14 15:50 +0200
        Re: [PATCH v2 07/13] sched/fair: Let asymmetric cpu configurations  balance at wake-up Morten Rasmussen <morten.rasmussen@arm.com> - 2016-07-15 10:40 +0200

#1442421 — Re: [PATCH v2 07/13] sched/fair: Let asymmetric cpu configurations balance at wake-up

On 22 June 2016 at 19:03, Morten Rasmussen <morten.rasmussen@arm.com> wrote:
> Currently, SD_WAKE_AFFINE always takes priority over wakeup balancing if
> SD_BALANCE_WAKE is set on the sched_domains. For asymmetric
> configurations SD_WAKE_AFFINE is only desirable if the waking task's
> compute demand (utilization) is suitable for all the cpu capacities
> available within the SD_WAKE_AFFINE sched_domain. If not, let wakeup

instead of "suitable for all the cpu capacities available within the
SD_WAKE_AFFINE sched_domain", should it be "suitable for local cpu and
prev cpu" becasue you only check the capacity of these 2 CPUs.

Other than this comment for the commit message, the patch looks good to me
Acked-by: Vincent Guittot <vincent.guittot@linaro.org>

> balancing take over (find_idlest_{group, cpu}()).
>
> This patch makes affine wake-ups conditional on whether both the waker
> cpu and prev_cpu has sufficient capacity for the waking task, or not.
>
> It is assumed that the sched_group(s) containing the waker cpu and
> prev_cpu only contain cpu with the same capacity (homogeneous).
>
> Ideally, we shouldn't set 'want_affine' in the first place, but we don't
> know if SD_BALANCE_WAKE is enabled on the sched_domain(s) until we start
> traversing them.
>
> 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 | 28 +++++++++++++++++++++++++++-
>  1 file changed, 27 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 216db302e87d..dba02c7b57b3 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -114,6 +114,12 @@ unsigned int __read_mostly sysctl_sched_shares_window = 10000000UL;
>  unsigned int sysctl_sched_cfs_bandwidth_slice = 5000UL;
>  #endif
>
> +/*
> + * The margin used when comparing utilization with cpu capacity:
> + * util * 1024 < capacity * margin
> + */
> +unsigned int capacity_margin = 1280; /* ~20% */
> +
>  static inline void update_load_add(struct load_weight *lw, unsigned long inc)
>  {
>         lw->weight += inc;
> @@ -5260,6 +5266,25 @@ static int cpu_util(int cpu)
>         return (util >= capacity) ? capacity : util;
>  }
>
> +static inline int task_util(struct task_struct *p)
> +{
> +       return p->se.avg.util_avg;
> +}
> +
> +static int wake_cap(struct task_struct *p, int cpu, int prev_cpu)
> +{
> +       long min_cap, max_cap;
> +
> +       min_cap = min(capacity_orig_of(prev_cpu), capacity_orig_of(cpu));
> +       max_cap = cpu_rq(cpu)->rd->max_cpu_capacity;
> +
> +       /* Minimum capacity is close to max, no need to abort wake_affine */
> +       if (max_cap - min_cap < max_cap >> 3)
> +               return 0;
> +
> +       return min_cap * 1024 < task_util(p) * capacity_margin;
> +}
> +
>  /*
>   * select_task_rq_fair: Select target runqueue for the waking task in domains
>   * that have the 'sd_flag' flag set. In practice, this is SD_BALANCE_WAKE,
> @@ -5283,7 +5308,8 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
>
>         if (sd_flag & SD_BALANCE_WAKE) {
>                 record_wakee(p);
> -               want_affine = !wake_wide(p) && cpumask_test_cpu(cpu, tsk_cpus_allowed(p));
> +               want_affine = !wake_wide(p) && !wake_cap(p, cpu, prev_cpu)
> +                             && cpumask_test_cpu(cpu, tsk_cpus_allowed(p));
>         }
>
>         rcu_read_lock();
> --
> 1.9.1
>

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#1442588

On Wed, Jul 13, 2016 at 02:56:41PM +0200, Vincent Guittot wrote:
> On 22 June 2016 at 19:03, Morten Rasmussen <morten.rasmussen@arm.com> wrote:
> > Currently, SD_WAKE_AFFINE always takes priority over wakeup balancing if
> > SD_BALANCE_WAKE is set on the sched_domains. For asymmetric
> > configurations SD_WAKE_AFFINE is only desirable if the waking task's
> > compute demand (utilization) is suitable for all the cpu capacities
> > available within the SD_WAKE_AFFINE sched_domain. If not, let wakeup
> 
> instead of "suitable for all the cpu capacities available within the
> SD_WAKE_AFFINE sched_domain", should it be "suitable for local cpu and
> prev cpu" becasue you only check the capacity of these 2 CPUs.

Good point. I currently make the implicit assumption that capacity of local cpu
and prev cpu represent the capacity for all cpus their SD_WAKE_AFFINE
domains. It breaks if you should choose to have SD_WAKE_AFFINE on a
domain that spans both little and big cpus, as if local/prev cpu happens
to be big we assume that they are all big and let select_idle_sibling()
handle the task placement even for big tasks if local/prev cpu are both
big.

I don't see why anybody would want that kind of setup, but I think the
assumption should still be written down somewhere, either here or in a
comment in wake_cap() or both.

The next paragraph in the commit message mentions that we actually only
check waker cpu and prev_cpu capacity. Would it be more clear if we
extend that to something like:

    This patch makes affine wake-ups conditional on whether both the waker
    cpu and prev_cpu has sufficient capacity for the waking task, or
    not, assuming that the cpu capacities within an SD_WAKE_AFFINE
    domain are homogeneous.

Thoughts?

> 
> Other than this comment for the commit message, the patch looks good to me
> Acked-by: Vincent Guittot <vincent.guittot@linaro.org>

Thanks,
Morten


> 
> > balancing take over (find_idlest_{group, cpu}()).
> >
> > This patch makes affine wake-ups conditional on whether both the waker
> > cpu and prev_cpu has sufficient capacity for the waking task, or not.
> >
> > It is assumed that the sched_group(s) containing the waker cpu and
> > prev_cpu only contain cpu with the same capacity (homogeneous).
> >
> > Ideally, we shouldn't set 'want_affine' in the first place, but we don't
> > know if SD_BALANCE_WAKE is enabled on the sched_domain(s) until we start
> > traversing them.
> >
> > 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 | 28 +++++++++++++++++++++++++++-
> >  1 file changed, 27 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 216db302e87d..dba02c7b57b3 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -114,6 +114,12 @@ unsigned int __read_mostly sysctl_sched_shares_window = 10000000UL;
> >  unsigned int sysctl_sched_cfs_bandwidth_slice = 5000UL;
> >  #endif
> >
> > +/*
> > + * The margin used when comparing utilization with cpu capacity:
> > + * util * 1024 < capacity * margin
> > + */
> > +unsigned int capacity_margin = 1280; /* ~20% */
> > +
> >  static inline void update_load_add(struct load_weight *lw, unsigned long inc)
> >  {
> >         lw->weight += inc;
> > @@ -5260,6 +5266,25 @@ static int cpu_util(int cpu)
> >         return (util >= capacity) ? capacity : util;
> >  }
> >
> > +static inline int task_util(struct task_struct *p)
> > +{
> > +       return p->se.avg.util_avg;
> > +}
> > +
> > +static int wake_cap(struct task_struct *p, int cpu, int prev_cpu)
> > +{
> > +       long min_cap, max_cap;
> > +
> > +       min_cap = min(capacity_orig_of(prev_cpu), capacity_orig_of(cpu));
> > +       max_cap = cpu_rq(cpu)->rd->max_cpu_capacity;
> > +
> > +       /* Minimum capacity is close to max, no need to abort wake_affine */
> > +       if (max_cap - min_cap < max_cap >> 3)
> > +               return 0;
> > +
> > +       return min_cap * 1024 < task_util(p) * capacity_margin;
> > +}
> > +
> >  /*
> >   * select_task_rq_fair: Select target runqueue for the waking task in domains
> >   * that have the 'sd_flag' flag set. In practice, this is SD_BALANCE_WAKE,
> > @@ -5283,7 +5308,8 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
> >
> >         if (sd_flag & SD_BALANCE_WAKE) {
> >                 record_wakee(p);
> > -               want_affine = !wake_wide(p) && cpumask_test_cpu(cpu, tsk_cpus_allowed(p));
> > +               want_affine = !wake_wide(p) && !wake_cap(p, cpu, prev_cpu)
> > +                             && cpumask_test_cpu(cpu, tsk_cpus_allowed(p));
> >         }
> >
> >         rcu_read_lock();
> > --
> > 1.9.1
> >

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#1443465

On 13 July 2016 at 18:14, Morten Rasmussen <morten.rasmussen@arm.com> wrote:
> On Wed, Jul 13, 2016 at 02:56:41PM +0200, Vincent Guittot wrote:
>> On 22 June 2016 at 19:03, Morten Rasmussen <morten.rasmussen@arm.com> wrote:
>> > Currently, SD_WAKE_AFFINE always takes priority over wakeup balancing if
>> > SD_BALANCE_WAKE is set on the sched_domains. For asymmetric
>> > configurations SD_WAKE_AFFINE is only desirable if the waking task's
>> > compute demand (utilization) is suitable for all the cpu capacities
>> > available within the SD_WAKE_AFFINE sched_domain. If not, let wakeup
>>
>> instead of "suitable for all the cpu capacities available within the
>> SD_WAKE_AFFINE sched_domain", should it be "suitable for local cpu and
>> prev cpu" becasue you only check the capacity of these 2 CPUs.
>
> Good point. I currently make the implicit assumption that capacity of local cpu
> and prev cpu represent the capacity for all cpus their SD_WAKE_AFFINE
> domains. It breaks if you should choose to have SD_WAKE_AFFINE on a
> domain that spans both little and big cpus, as if local/prev cpu happens
> to be big we assume that they are all big and let select_idle_sibling()
> handle the task placement even for big tasks if local/prev cpu are both
> big.

Isn't the sd_llc used in select_idle_sibling and not the
SD_WAKE_AFFINE domian so if CPUs in the sd_llc are homogeneous, we are
safe

>
> I don't see why anybody would want that kind of setup, but I think the
> assumption should still be written down somewhere, either here or in a
> comment in wake_cap() or both.
>
> The next paragraph in the commit message mentions that we actually only
> check waker cpu and prev_cpu capacity. Would it be more clear if we
> extend that to something like:
>
>     This patch makes affine wake-ups conditional on whether both the waker
>     cpu and prev_cpu has sufficient capacity for the waking task, or
>     not, assuming that the cpu capacities within an SD_WAKE_AFFINE
>     domain are homogeneous.
>
> Thoughts?
>
>>
>> Other than this comment for the commit message, the patch looks good to me
>> Acked-by: Vincent Guittot <vincent.guittot@linaro.org>
>
> Thanks,
> Morten
>
>
>>
>> > balancing take over (find_idlest_{group, cpu}()).
>> >
>> > This patch makes affine wake-ups conditional on whether both the waker
>> > cpu and prev_cpu has sufficient capacity for the waking task, or not.
>> >
>> > It is assumed that the sched_group(s) containing the waker cpu and
>> > prev_cpu only contain cpu with the same capacity (homogeneous).
>> >
>> > Ideally, we shouldn't set 'want_affine' in the first place, but we don't
>> > know if SD_BALANCE_WAKE is enabled on the sched_domain(s) until we start
>> > traversing them.
>> >
>> > 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 | 28 +++++++++++++++++++++++++++-
>> >  1 file changed, 27 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> > index 216db302e87d..dba02c7b57b3 100644
>> > --- a/kernel/sched/fair.c
>> > +++ b/kernel/sched/fair.c
>> > @@ -114,6 +114,12 @@ unsigned int __read_mostly sysctl_sched_shares_window = 10000000UL;
>> >  unsigned int sysctl_sched_cfs_bandwidth_slice = 5000UL;
>> >  #endif
>> >
>> > +/*
>> > + * The margin used when comparing utilization with cpu capacity:
>> > + * util * 1024 < capacity * margin
>> > + */
>> > +unsigned int capacity_margin = 1280; /* ~20% */
>> > +
>> >  static inline void update_load_add(struct load_weight *lw, unsigned long inc)
>> >  {
>> >         lw->weight += inc;
>> > @@ -5260,6 +5266,25 @@ static int cpu_util(int cpu)
>> >         return (util >= capacity) ? capacity : util;
>> >  }
>> >
>> > +static inline int task_util(struct task_struct *p)
>> > +{
>> > +       return p->se.avg.util_avg;
>> > +}
>> > +
>> > +static int wake_cap(struct task_struct *p, int cpu, int prev_cpu)
>> > +{
>> > +       long min_cap, max_cap;
>> > +
>> > +       min_cap = min(capacity_orig_of(prev_cpu), capacity_orig_of(cpu));
>> > +       max_cap = cpu_rq(cpu)->rd->max_cpu_capacity;
>> > +
>> > +       /* Minimum capacity is close to max, no need to abort wake_affine */
>> > +       if (max_cap - min_cap < max_cap >> 3)
>> > +               return 0;
>> > +
>> > +       return min_cap * 1024 < task_util(p) * capacity_margin;
>> > +}
>> > +
>> >  /*
>> >   * select_task_rq_fair: Select target runqueue for the waking task in domains
>> >   * that have the 'sd_flag' flag set. In practice, this is SD_BALANCE_WAKE,
>> > @@ -5283,7 +5308,8 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
>> >
>> >         if (sd_flag & SD_BALANCE_WAKE) {
>> >                 record_wakee(p);
>> > -               want_affine = !wake_wide(p) && cpumask_test_cpu(cpu, tsk_cpus_allowed(p));
>> > +               want_affine = !wake_wide(p) && !wake_cap(p, cpu, prev_cpu)
>> > +                             && cpumask_test_cpu(cpu, tsk_cpus_allowed(p));
>> >         }
>> >
>> >         rcu_read_lock();
>> > --
>> > 1.9.1
>> >

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#1444061

On Thu, Jul 14, 2016 at 03:45:17PM +0200, Vincent Guittot wrote:
> On 13 July 2016 at 18:14, Morten Rasmussen <morten.rasmussen@arm.com> wrote:
> > On Wed, Jul 13, 2016 at 02:56:41PM +0200, Vincent Guittot wrote:
> >> On 22 June 2016 at 19:03, Morten Rasmussen <morten.rasmussen@arm.com> wrote:
> >> > Currently, SD_WAKE_AFFINE always takes priority over wakeup balancing if
> >> > SD_BALANCE_WAKE is set on the sched_domains. For asymmetric
> >> > configurations SD_WAKE_AFFINE is only desirable if the waking task's
> >> > compute demand (utilization) is suitable for all the cpu capacities
> >> > available within the SD_WAKE_AFFINE sched_domain. If not, let wakeup
> >>
> >> instead of "suitable for all the cpu capacities available within the
> >> SD_WAKE_AFFINE sched_domain", should it be "suitable for local cpu and
> >> prev cpu" becasue you only check the capacity of these 2 CPUs.
> >
> > Good point. I currently make the implicit assumption that capacity of local cpu
> > and prev cpu represent the capacity for all cpus their SD_WAKE_AFFINE
> > domains. It breaks if you should choose to have SD_WAKE_AFFINE on a
> > domain that spans both little and big cpus, as if local/prev cpu happens
> > to be big we assume that they are all big and let select_idle_sibling()
> > handle the task placement even for big tasks if local/prev cpu are both
> > big.
> 
> Isn't the sd_llc used in select_idle_sibling and not the
> SD_WAKE_AFFINE domian so if CPUs in the sd_llc are homogeneous, we are
> safe

Yes, I confused myself (again) with SD_WAKE_AFFINE and sd_llc in the
above. It should have been sd_llc instead of SD_WAKE_AFFINE. I will fix
the commit message to be correct.

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