From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>, Mike Galbraith <efault@gmx.de>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 2/3] sched: Unloop sched avg decaying
Date: Thu, 30 Jun 2016 15:20:37 +0200 [thread overview]
Message-ID: <20160630132037.GE30921@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20160630125225.GA32568@lerouge>
On Thu, Jun 30, 2016 at 02:52:26PM +0200, Frederic Weisbecker wrote:
> On Tue, Jun 14, 2016 at 05:58:42PM +0200, Peter Zijlstra wrote:
> > Why not add the division to the nohz exit path only?
>
> It would be worse I think because we may exit much more often from nohz
> than we reach a sched_avg_period().
>
> So the only safe optimization I can do for now is:
How about something like this then?
---
kernel/sched/core.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3387e4f14fc9..fd1ae4c4105f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -665,9 +665,23 @@ bool sched_can_stop_tick(struct rq *rq)
void sched_avg_update(struct rq *rq)
{
- s64 period = sched_avg_period();
+ s64 delta, period = sched_avg_period();
- while ((s64)(rq_clock(rq) - rq->age_stamp) > period) {
+ delta = (s64)(rq_clock(rq) - rq->age_stamp);
+ if (likely(delta < period))
+ return;
+
+ if (unlikely(delta > 3*period)) {
+ int pending;
+ u64 rem;
+
+ pending = div64_u64_rem(delta, period, &rem);
+ rq->age_stamp += delta - rem;
+ rq->rt_avg >>= pending;
+ return;
+ }
+
+ while (delta > period) {
/*
* Inline assembly required to prevent the compiler
* optimising this loop into a divmod call.
@@ -675,6 +689,7 @@ void sched_avg_update(struct rq *rq)
*/
asm("" : "+rm" (rq->age_stamp));
rq->age_stamp += period;
+ delta -= period;
rq->rt_avg /= 2;
}
}
next prev parent reply other threads:[~2016-06-30 13:52 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-14 15:27 [PATCH 0/3] sched: Enhance/fix sched_avg_update() Frederic Weisbecker
2016-06-14 15:28 ` [PATCH 1/3] sched: Introduce sched_time_avg_ns minimal value Frederic Weisbecker
2016-06-14 15:28 ` [PATCH 2/3] sched: Unloop sched avg decaying Frederic Weisbecker
2016-06-14 15:58 ` Peter Zijlstra
2016-06-30 12:52 ` Frederic Weisbecker
2016-06-30 13:20 ` Peter Zijlstra [this message]
2016-07-06 11:53 ` Frederic Weisbecker
2016-06-14 15:28 ` [NOT-FOR-MERGE-PATCH 3/3] Debug: Alternate old/new version of sched_avg_update calls for profiling Frederic Weisbecker
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