Currently, the decayed values of previous periods can spill into the lower 10
bits of
runnable_avg_period. This makes the next period to be less than 1024 us. If we
want
to decay exactly every 1024us, which I see no reason not to (less math overhead
and
consistent decay period among all tasks), we can use a separate field to track
how
much time the current period has elapsed instead of overloading
runnable_avg_period.
This patch achieves this.
Signed-off-by: Zhihui Zhang <zzhs...@gmail.com>
---
include/linux/sched.h | 2 +-
kernel/sched/fair.c | 5 ++++-
2 files changed, 5 insertions(+), 2 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8db31ef..fa6b23b 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1116,7 +1116,7 @@ struct sched_avg {
* above by 1024/(1-y). Thus we only need a u32 to store them for all
* choices of y < 1-2^(-32)*1024.
*/
- u32 runnable_avg_sum, runnable_avg_period;
+ u32 accrue, runnable_avg_sum, runnable_avg_period;
u64 last_runnable_update;
s64 decay_count;
unsigned long load_avg_contrib;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index df2cdf7..c87ecf5 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -676,6 +676,7 @@ void init_task_runnable_average(struct task_struct *p)
{
u32 slice;
+ p->se.avg.accrue = 0;
p->se.avg.decay_count = 0;
slice = sched_slice(task_cfs_rq(p), &p->se) >> 10;
p->se.avg.runnable_avg_sum = slice;
@@ -2526,11 +2527,12 @@ static __always_inline int
__update_entity_runnable_avg(u64 now,
sa->last_runnable_update = now;
/* delta_w is the amount already accumulated against our next period */
- delta_w = sa->runnable_avg_period % 1024;
+ delta_w = sa->accrue;
if (delta + delta_w >= 1024) {
/* period roll-over */
decayed = 1;
+ sa->accrue = 0;
/*
* Now that we know we're crossing a period boundary, figure
* out how much from delta we need to complete the current
@@ -2558,6 +2560,7 @@ static __always_inline int
__update_entity_runnable_avg(u64 now,
sa->runnable_avg_sum += runnable_contrib;
sa->runnable_avg_period += runnable_contrib;
}
+ sa->accrue += delta;
/* Remainder of delta accrued against u_0` */
if (runnable)
--
1.9.1
--
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