Re: [PATCH] sched: Folding nohz load accounting more accurate

Charles Wang
2012-06-18T14:41:59Z

Peter's patch works the well. Now I ported the second patch
to fix high load problem based on Peter's. It works fine on my testing
environment. Doug, please try this. Thanks.

In our mind per-cpu sampling for cpu idle and non-idle is equal. But
actually may not. For non-idle cpu sampling, it's right the load when
sampling. But for idle, cause of nohz, the sampling will be delayed to
nohz exit(less than 1 tick after nohz exit). Nohz exit is always caused
by processes woken up--non-idle model. It's not fair here. Idle
sampling will be turned to non-idle sampling. And cause loadavg being
higher than normal.

time-expected-sampling
| time-do-sampling
| |
V V
-|-------------------------|--
start_nohz stop_nohz

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4101a0e..180e612 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2228,6 +2228,7 @@ void calc_load_account_idle(struct rq *this_rq)
int idx;

delta = calc_load_fold_active(this_rq);
+ this_rq->last_idle_enter = jiffies;

if (delta) {
idx = calc_load_write_idx();
atomic_long_add(delta, &calc_load_idle[idx]);
@@ -2431,15 +2432,27 @@ void calc_global_load(void)
static void calc_load_account_active(struct rq *this_rq)
{
long delta;
+ unsigned long delta_time;
+ long last_idle_time_elapse;

if (time_before(jiffies, this_rq->calc_load_update))
return;

+ last_idle_time_elapse = this_rq->last_idle_enter - calc_load_update;
+ delta_time = jiffies - this_rq->calc_load_update;
+
+ if (last_idle_time_elapse > 0)
+ goto out;
+
+ if ((last_idle_time_elapse > -1) && (delta_time >= 1))
+ goto out;
+
delta = calc_load_fold_active(this_rq);
delta += calc_load_fold_idle();
if (delta)
atomic_long_add(delta, &calc_load_tasks);

+out:
this_rq->calc_load_update += LOAD_FREQ;
}

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 4134d37..a356588 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -438,6 +438,7 @@ struct rq {

/* calc_load related fields */
unsigned long calc_load_update;
+ unsigned long last_idle_enter;
long calc_load_active;

#ifdef CONFIG_SCHED_HRTICK
--
1.7.9.5