Messages in this thread | | | Subject | Re: netperf ~50% regression with 2.6.33-rc1, bisect to 1b9508f | From | Mike Galbraith <> | Date | Mon, 25 Jan 2010 12:35:42 +0100 |
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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?
So. Rummaging around doing absolutely _nothing_ useful, there being zero movable tasks in this load, prevents us switching to the idle thread before the scheduling task is requeued. Oh joy.
Hm.... <imagines Peter's reaction to a busy wait> :) OTOH, that's what it's _doing_ with above patch.
-Mike
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