RE: Mainline kernel OLTP performance update

[Chris Mason <chris.mason@oracle.com>]

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
 	/*