Messages in this thread | | | Subject | Re: netperf ~50% regression with 2.6.33-rc1, bisect to 1b9508f | From | Lin Ming <> | Date | Tue, 26 Jan 2010 17:03:01 +0800 |
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On Mon, 2010-01-25 at 19:35 +0800, Mike Galbraith wrote: > On Mon, 2010-01-25 at 18:03 +0800, Lin Ming wrote: > > > With above commit, the idle balance was rate limited, so CPU 15(server, > > waiting data from client) is idle at most time. > > > > CPU0(client) executes as below, > > > > try_to_wake_up > > check_preempt_curr_idle > > resched_task > > smp_send_reschedule > > > > This causes a lot of rescheduling IPI. > > > > This commit can't be reverted due to conflict, so I just add below code > > to disable "Rate-limit newidle" and the performance was recovered. > > > > diff --git a/kernel/sched.c b/kernel/sched.c > > index 18cceee..588fdef 100644 > > --- a/kernel/sched.c > > +++ b/kernel/sched.c > > @@ -4421,9 +4421,6 @@ static void idle_balance(int this_cpu, struct rq *this_rq) > > > > this_rq->idle_stamp = this_rq->clock; > > > > - if (this_rq->avg_idle < sysctl_sched_migration_cost) > > - return; > > - > > for_each_domain(this_cpu, sd) { > > unsigned long interval; > > > > Heh, so you should see the same thing with newidle disabled, as it was > in .31 and many kernels prior. Do you?
Weird. 2.6.31 does not have so many reschedule IPI.
This Nehalem machine has 3 domain levels, $ grep . cpu0/domain*/name cpu0/domain0/name:SIBLING cpu0/domain1/name:MC cpu0/domain2/name:NODE
For 2.6.31, SD_BALANCE_NEWIDLE is only set on SIBLING level. For 2.6.32-rc1, SD_BALANCE_NEWIDLE is set on all 3 levels.
I can see many reschedule IPI in 2.6.32-rc1 if SD_BALANCE_NEWIDLE is cleared for all 3 levels. But for 2.6.31, I didn't see so many IPI even SD_BALANCE_NEWIDLE is cleared on SIBLING level.
So it seems something happens between 2.6.31 and 2.6.32-rc1. I'll bisect ...
Lin Ming
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