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

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

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()?

							Thanx, Paul