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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