On Fri, May 23, 2014 at 05:53:04PM +0200, Vincent Guittot wrote:
> If the CPU is used for handling lot of IRQs, trig a load balance to check if
> it's worth moving its tasks on another CPU that has more capacity
>
> Signed-off-by: Vincent Guittot <[email protected]>
> ---
> kernel/sched/fair.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index e8a30f9..2501e49 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5948,6 +5948,13 @@ static bool update_sd_pick_busiest(struct lb_env *env,
> if (sgs->sum_nr_running > sgs->group_capacity)
> return true;
>
> + /*
> + * The group capacity is reduced probably because of activity from other
> + * sched class or interrupts which use part of the available capacity
> + */
> + if ((sg->sgp->power_orig * 100) > (sgs->group_power *
> env->sd->imbalance_pct))
> + return true;
> +
> if (sgs->group_imb)
> return true;
>
But we should already do this because the load numbers are scaled with
the power/capacity figures. If one CPU gets significant less time to run
fair tasks, its effective load would spike and it'd get to be selected
here anyway.
Or am I missing something?
> @@ -7282,6 +7289,12 @@ static inline int nohz_kick_needed(struct rq *rq)
>
> if (nr_busy > 1)
> goto need_kick_unlock;
> +
> + if ((rq->cfs.h_nr_running >= 1)
> + && ((rq->cpu_power * sd->imbalance_pct) <
> + (rq->cpu_power_orig * 100)))
> + goto need_kick_unlock;
> +
> }
>
> sd = rcu_dereference(per_cpu(sd_asym, cpu));
OK, so there you're kicking the idle balancer to try and get another CPU
to pull some load? That makes sense I suppose.
That function is pretty horrible though; how about something like this
first?
---
kernel/sched/fair.c | 29 +++++++++++++----------------
1 file changed, 13 insertions(+), 16 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c9617b73bcc0..47fb96e6fa83 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7215,15 +7215,16 @@ static void nohz_idle_balance(struct rq *this_rq, enum
cpu_idle_type idle)
* - For SD_ASYM_PACKING, if the lower numbered cpu's in the scheduler
* domain span are idle.
*/
-static inline int nohz_kick_needed(struct rq *rq)
+static inline bool nohz_kick_needed(struct rq *rq)
{
unsigned long now = jiffies;
struct sched_domain *sd;
struct sched_group_power *sgp;
int nr_busy, cpu = rq->cpu;
+ bool kick = false;
if (unlikely(rq->idle_balance))
- return 0;
+ return false;
/*
* We may be recently in ticked or tickless idle mode. At the first
@@ -7237,38 +7238,34 @@ static inline int nohz_kick_needed(struct rq *rq)
* balancing.
*/
if (likely(!atomic_read(&nohz.nr_cpus)))
- return 0;
+ return false;
if (time_before(now, nohz.next_balance))
- return 0;
+ return false;
if (rq->nr_running >= 2)
- goto need_kick;
+ return true;
rcu_read_lock();
sd = rcu_dereference(per_cpu(sd_busy, cpu));
-
if (sd) {
sgp = sd->groups->sgp;
nr_busy = atomic_read(&sgp->nr_busy_cpus);
- if (nr_busy > 1)
- goto need_kick_unlock;
+ if (nr_busy > 1) {
+ kick = true;
+ goto unlock;
+ }
}
sd = rcu_dereference(per_cpu(sd_asym, cpu));
-
if (sd && (cpumask_first_and(nohz.idle_cpus_mask,
sched_domain_span(sd)) < cpu))
- goto need_kick_unlock;
-
- rcu_read_unlock();
- return 0;
+ kick = true;
-need_kick_unlock:
+unlock:
rcu_read_unlock();
-need_kick:
- return 1;
+ return kick;
}
#else
static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) { }
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