From: Morten Rasmussen <morten.rasmussen@arm.com>
To: Wanpeng Li <kernellwp@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
yuyang.du@intel.com, Vincent Guittot <vincent.guittot@linaro.org>,
Mike Galbraith <mgalbraith@suse.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 09/16] sched/fair: Let asymmetric cpu configurations balance at wake-up
Date: Wed, 25 May 2016 10:49:50 +0100 [thread overview]
Message-ID: <20160525094949.GL27946@e105550-lin.cambridge.arm.com> (raw)
In-Reply-To: <CANRm+CxiUE6VkGie89EpKY_cvzcXusPRHE8M91q+TUw3DMg_Mw@mail.gmail.com>
On Wed, May 25, 2016 at 02:57:00PM +0800, Wanpeng Li wrote:
> 2016-05-23 18:58 GMT+08:00 Morten Rasmussen <morten.rasmussen@arm.com>:
> > 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 the cpu capacities
> > available within the SD_WAKE_AFFINE sched_domain. If not, let wakeup
> > balancing take over (find_idlest_{group, cpu}()).
> >
> > The assumption is that SD_WAKE_AFFINE is never set for a sched_domain
> > containing cpus with different capacities. This is enforced by a
> > previous patch based on the SD_ASYM_CPUCAPACITY flag.
> >
> > 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 564215d..ce44fa7 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;
> > @@ -5293,6 +5299,25 @@ 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 delta;
> > + long prev_cap = capacity_of(prev_cpu);
> > +
> > + delta = cpu_rq(cpu)->rd->max_cpu_capacity - prev_cap;
> > +
> > + /* prev_cpu is fairly close to max, no need to abort wake_affine */
> > + if (delta < prev_cap >> 3)
> > + return 0;
> > +
> > + return prev_cap * 1024 < task_util(p) * capacity_margin;
> > +}
>
> If one task util_avg is SCHED_CAPACITY_SCALE and running on x86 box w/
> SMT enabled, then each HT has capacity 589, wake_cap() will result in
> always not wake affine, right?
The idea is that SMT systems would bail out already at the previous
condition. We should have max_cpu_capacity == prev_cap == 589, delta
should then be zero and make the first condition true and make
wake_cap() always return 0 for any system with symmetric capacities
regardless of their actual capacity values.
Note that this isn't entirely true as I used capacity_of() for prev_cap,
if I change that to capacity_orig_of() it should be true.
By making the !wake_cap() condition always true for want_affine, we
should preserve existing behaviour for SMT/SMP. The only overhead is the
capacity delta computation and comparison, which should be cheap.
Does that make sense?
Btw, task util_avg == SCHED_CAPACITY_SCALE should only be possible
temporarily, it should decay to util_avg <=
capacity_orig_of(task_cpu(p)) over time. That doesn't affect your
question though as the second condition would still evaluate true if
util_avg == capacity_orig_of(task_cpu(p)), but as said above the first
condition should bail out before we get here.
Morten
> > +
> > /*
> > * 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,
> > @@ -5316,7 +5341,8 @@ 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
> >
next prev parent reply other threads:[~2016-05-25 9:49 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-23 10:58 [PATCH 00/16] sched: Clean-ups and asymmetric cpu capacity support Morten Rasmussen
2016-05-23 10:58 ` [PATCH 01/16] sched: Fix power to capacity renaming in comment Morten Rasmussen
2016-05-23 10:58 ` [PATCH 02/16] sched/fair: Consistent use of prev_cpu in wakeup path Morten Rasmussen
2016-06-01 19:49 ` Peter Zijlstra
2016-05-23 10:58 ` [PATCH 03/16] sched/fair: Disregard idle task wakee_flips in wake_wide Morten Rasmussen
2016-05-23 11:12 ` Mike Galbraith
2016-05-23 12:00 ` Morten Rasmussen
2016-05-23 13:00 ` Mike Galbraith
2016-05-23 14:10 ` Morten Rasmussen
2016-05-23 15:42 ` Mike Galbraith
2016-05-23 23:17 ` Yuyang Du
2016-05-23 23:04 ` Yuyang Du
2016-06-01 19:57 ` Peter Zijlstra
2016-06-02 8:05 ` Peter Zijlstra
2016-06-07 12:08 ` Morten Rasmussen
2016-05-23 10:58 ` [PATCH 04/16] sched/fair: Optimize find_idlest_cpu() when there is no choice Morten Rasmussen
2016-05-24 6:29 ` Mike Galbraith
2016-05-24 8:05 ` Morten Rasmussen
2016-05-24 8:12 ` Mike Galbraith
2016-06-01 19:59 ` Peter Zijlstra
2016-06-07 14:25 ` Morten Rasmussen
2016-05-23 10:58 ` [PATCH 05/16] sched: Introduce SD_ASYM_CPUCAPACITY sched_domain topology flag Morten Rasmussen
2016-05-23 10:58 ` [PATCH 06/16] sched: Disable WAKE_AFFINE for asymmetric configurations Morten Rasmussen
2016-05-24 9:10 ` Vincent Guittot
2016-05-24 10:29 ` Morten Rasmussen
2016-05-24 12:12 ` Vincent Guittot
2016-05-24 13:16 ` Morten Rasmussen
2016-05-24 13:27 ` Vincent Guittot
2016-05-24 13:36 ` Morten Rasmussen
2016-05-24 13:52 ` Vincent Guittot
2016-05-24 15:02 ` Morten Rasmussen
2016-05-24 15:53 ` Vincent Guittot
2016-05-25 9:12 ` Morten Rasmussen
2016-05-26 6:45 ` Vincent Guittot
2016-06-07 16:50 ` Morten Rasmussen
2016-05-23 10:58 ` [PATCH 07/16] sched: Make SD_BALANCE_WAKE a topology flag Morten Rasmussen
2016-05-24 23:52 ` Yuyang Du
2016-05-25 9:27 ` Morten Rasmussen
2016-06-01 20:18 ` Peter Zijlstra
2016-06-08 8:45 ` Morten Rasmussen
2016-05-23 10:58 ` [PATCH 08/16] sched: Store maximum per-cpu capacity in root domain Morten Rasmussen
2016-05-23 10:58 ` [PATCH 09/16] sched/fair: Let asymmetric cpu configurations balance at wake-up Morten Rasmussen
2016-05-24 0:04 ` Yuyang Du
2016-05-24 8:10 ` Morten Rasmussen
2016-05-24 7:03 ` Mike Galbraith
2016-05-24 7:15 ` Mike Galbraith
2016-05-25 6:57 ` Wanpeng Li
2016-05-25 9:49 ` Morten Rasmussen [this message]
2016-05-25 10:29 ` Wanpeng Li
2016-05-25 10:54 ` Morten Rasmussen
2016-05-25 11:18 ` Wanpeng Li
2016-06-02 14:21 ` Peter Zijlstra
2016-06-08 11:29 ` Morten Rasmussen
2016-06-08 14:36 ` Peter Zijlstra
2016-05-23 10:58 ` [PATCH 10/16] sched/fair: Compute task/cpu utilization at wake-up more correctly Morten Rasmussen
2016-05-23 10:58 ` [PATCH 11/16] sched/fair: Consider spare capacity in find_idlest_group() Morten Rasmussen
2016-05-23 10:58 ` [PATCH 12/16] sched: Add per-cpu max capacity to sched_group_capacity Morten Rasmussen
2016-05-23 10:58 ` [PATCH 13/16] sched/fair: Avoid pulling tasks from non-overloaded higher capacity groups Morten Rasmussen
2016-05-23 10:58 ` [PATCH 14/16] arm: Set SD_ASYM_CPUCAPACITY for big.LITTLE platforms Morten Rasmussen
2016-05-23 10:58 ` [PATCH 15/16] arm: Set SD_BALANCE_WAKE flag for asymmetric capacity systems Morten Rasmussen
2016-05-23 10:58 ` [PATCH 16/16] arm: Update arch_scale_cpu_capacity() to reflect change to define Morten Rasmussen
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