Re: 2.6.24-rc8-rt1: Strange latencies on mpc5200 powerpc - RCU issue?

[Wolfgang Grandegger]

Paul E. McKenney wrote:
> On Wed, Jul 02, 2008 at 01:03:27PM +0200, Wolfgang Grandegger wrote:
> > Wolfgang Grandegger wrote:
> > > Steven Rostedt wrote:
> > > There seems to be something in trace_mark() keeping latency low:
> > >   http://lxr.linux.no/linux+v2.6.24.4/include/linux/marker.h#L52
> > > I will follow your suggestions.
> > I removed all "likely" and "unlikely" macros, but the latencies did not 
> > improve. Then I added
> >
> > 	preempt_disable();
> > 	preempt_enable();
> >
> > at the two locations mentioned above, like trace_mark() does,  and disabled 
> > CONFIG_RCU_TRACE. That helped to keep the latencies low, and it did for 
> > 2.6.25.8-rt7 as well. As I see it, adding preemption points seem to prevent 
> > high latencies.
>
> Interesting.  Perhaps a preempt_enable_no_resched() somewhere that
> should be preempt_enable()?

FYI, Thomas fixed the real problem a week ago and the patch went into 
2.6.24.7-rt16. See his mail with the subject "2.6.24.7-rt16".

Wolfgang.
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