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 vincent.guittot@linaro.org
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) { }