Messages in this thread | | | Subject | Re: [patch] Real-Time Preemption, -RT-2.6.10-rc1-mm3-V0.7.23 | From | Mark_H_Johnson@raytheon ... | Date | Tue, 9 Nov 2004 15:07:32 -0600 |
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>i have released the -V0.7.23 Real-Time Preemption patch, which can be >downloaded from the usual place: > > http://redhat.com/~mingo/realtime-preempt/
A few notes on results from running with this patch (well, actually -EA that Ingo provided separately).
[1] Build problems, separately reported to Ingo with CONFIG_PREEMPT_RT enabled on x86 and you have modules using kunmap_atomic. Fix by adding kunmap_virt and kmap_to_page to the list of exports.
[2] The live lock that I was having seems to have been killed based on an hour of testing (I could usually cause it in 5 minutes or less).
[3] I am not so sure that the latency tracing works. I do not get any trace output, even if I set preempt_max_latency to zero. I also noticed that /proc/sys/kernel/preempt_wakeup_timing was removed at .20 but not sure if that was deliberate. As a result, I have no reports from the kernel tracing.
[4] Application level latencies are OK but not great. X test - only 90% of CPU loops are within 100 usec of nominal value. In previous RT kernels I got > 99% with 100 usec. top test - looks much nicer than X test, but still have up to 30% overhead on CPU loop. network I/O tests - smoothest of all test results, very nice disk write - very noisy, bursts of long delays with only 82% within 100 usec and worst case has over 100% overhead (2.5 msec vs 1.16 nominal) disk copy - fewer bursts, but worst case is similar to disk write. About 95% within 100 usec. disk read - relatively clean with a pair of modest bursts early in the test and then settled out a little worse than the network tests. 99.9% of samples within 100 usec and max of 1.65 msec.
[5] concurrent ping of system had over 13% lost packets (1089 out of 10723 - plus I let this run after the tests had completed). The 2.4 RT kernel I use has no lost packets.
[6] I did a separate run of a script Ingo suggested that samples the kernel profile data. It shows basically no CPU time for the events/0 and events/1 tasks. I took 11 samples in about 1/2 hour of testing but nothing seems to jump out of the data.
--Mark H Johnson <mailto:Mark_H_Johnson@raytheon.com>
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