RE: Mainline kernel OLTP performance update

Chris Mason
2009-01-19T18:06:14Z

On Thu, 2009-01-15 at 00:11 -0700, Ma, Chinang wrote:
> >> > > > >
> >> > > > > Linux OLTP Performance summary
> >> > > > > Kernel# Speedup(x) Intr/s CtxSw/s us% sys% idle%
> >iowait%
> >> > > > > 2.6.24.2 1.000 21969 43425 76 24 0
> >0
> >> > > > > 2.6.27.2 0.973 30402 43523 74 25 0
> >1
> >> > > > > 2.6.29-rc1 0.965 30331 41970 74 26 0
> >0
> >> >
> >> > > But the interrupt rate went through the roof.
> >> >
> >> > Yes. I forget why that was; I'll have to dig through my archives for
> >> > that.
> >>
> >> Oh. I'd have thought that this alone could account for 3.5%.

A later email indicated the reschedule interrupt count doubled since
2.6.24, and so I poked around a bit at the causes of resched_task.

I think the -rt version of check_preempt_equal_prio has gotten much more
expensive since 2.6.24.

I'm sure these changes were made for good reasons, and this workload may
not be a good reason to change it back. But, what does the patch below
do to performance on 2.6.29-rcX?

-chris

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 954e1a8..bbe3492 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -842,6 +842,7 @@ static void check_preempt_curr_rt(struct rq *rq,
struct task_struct *p, int sync
resched_task(rq->curr);
return;
}
+ return;

#ifdef CONFIG_SMP
/*