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Subject[performance bug] volanomark regression on 37-rc1
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When do performance testing on 37-rc1 kernel on Core2 machines, we find
the volanomark loopback performance drop about 30%, that due to
commit:fab476228ba37907ad7

Volanomark link: http://www.volano.com/benchmarks.html
Our volanomark testing parameters as following:
"-count 25000 -rooms 10 "
JVM is jrockit-R27.3.1-jre1.5.0_11
java_options is "-Xmx1500m -Xms1500m -Xns750m -XXaggressive -Xlargepages
-XXlazyUnlocking -Xgc:genpar -XXtlasize:min=16k,preferred=64k"
and we set /proc/sys/kernel/sched_compat_yield as "1".

We find if with the following patch, the regression can be recovered.

Signed-off-by:Alex Shi <alex.shi@intel.com>

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index f4f6a83..5dca678 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1766,7 +1766,6 @@ static void pull_task(struct rq *src_rq, struct task_struct *p,
check_preempt_curr(this_rq, p, 0);

/* re-arm NEWIDLE balancing when moving tasks */
- src_rq->avg_idle = this_rq->avg_idle = 2*sysctl_sched_migration_cost;
this_rq->idle_stamp = 0;
}

It seems some of load_balance() is not necessary that caused by avg_idle
setting. But do not know more details of the volano running. Anyone like
to give a comments for this issue?

Ncrao, I have no idea of your benchmarks, but just guess removing the
avg_idle setting won't bring much wakeup delay for tasks. Could you like
to show some data of this?

The vmstat output for .36 and .37-rc1 kernel as below:
2.6.36
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
r b swpd free buff cache si so bi bo in cs us sy id wa st
394 0 0 4680728 3168 118972 0 0 0 3 5314 1348711 38 62 0 0 0
396 0 0 4680500 3184 118976 0 0 0 8 5345 1303237 38 62 0 0 0
413 0 0 4680252 3200 118976 0 0 0 3 5082 1326851 38 61 0 0 0
2.6.37-rc1
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
r b swpd free buff cache si so bi bo in cs us sy id wa st
329 0 0 4653748 4600 134032 0 0 0 7 11649 918370 35 64 0 0 0
210 0 0 4653492 4608 134032 0 0 0 6 11957 898011 36 64 0 0 0
373 0 0 4653496 4624 134032 0 0 0 4 11736 912468 36 64 0 0 0
Regards
Alex



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