On 07/09/15 13:42, Peter Zijlstra wrote:
> On Mon, Aug 31, 2015 at 11:24:49AM +0200, Peter Zijlstra wrote:
>
>> A quick run here gives:
>>
>> IVB-EP (2*20*2):
>
> As noted by someone; that should be 2*10*2, for a total of 40 cpus in
> this machine.
>
>>
>> perf stat --null --repeat 10 -- perf bench sched messaging -g 50 -l 5000
>>
>> Before: After:
>> 5.484170711 ( +- 0.74% ) 5.590001145 ( +- 0.45% )
>>
>> Which is an almost 2% slowdown :/
>>
>> I've yet to look at what happens.
>
> OK, so it appears this is link order nonsense. When I compared profiles
> between the series, the one function that had significant change was
> skb_release_data(), which doesn't make much sense.
>
> If I do a 'make clean' in front of each build, I get a repeatable
> improvement with this patch set (although how much of that is due to the
> patches itself or just because of code movement is as yet undetermined).
>
> I'm of a mind to apply these patches; with two patches on top, which
> I'll post shortly.
>
-- >8 --
From: Dietmar Eggemann <dietmar.eggem...@arm.com>
Date: Mon, 7 Sep 2015 14:57:22 +0100
Subject: [PATCH] sched/fair: Defer calling scaling functions
Do not call the scaling functions in case time goes backwards or the
last update of the sched_avg structure has happened less than 1024ns
ago.
Signed-off-by: Dietmar Eggemann <dietmar.eggem...@arm.com>
---
kernel/sched/fair.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d6ca8d987a63..3445d2fb38f4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2552,8 +2552,7 @@ __update_load_avg(u64 now, int cpu, struct sched_avg *sa,
u64 delta, scaled_delta, periods;
u32 contrib;
unsigned int delta_w, scaled_delta_w, decayed = 0;
- unsigned long scale_freq = arch_scale_freq_capacity(NULL, cpu);
- unsigned long scale_cpu = arch_scale_cpu_capacity(NULL, cpu);
+ unsigned long scale_freq, scale_cpu;
delta = now - sa->last_update_time;
/*
@@ -2574,6 +2573,9 @@ __update_load_avg(u64 now, int cpu, struct sched_avg *sa,
return 0;
sa->last_update_time = now;
+ scale_freq = arch_scale_freq_capacity(NULL, cpu);
+ scale_cpu = arch_scale_cpu_capacity(NULL, cpu);
+
/* delta_w is the amount already accumulated against our next period */
delta_w = sa->period_contrib;
if (delta + delta_w >= 1024) {
--
1.9.1
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