Hi, I am trying to experiment using 2.6.12 kernel with the realtime-preempt V0.7.51-38 patch to determine the kernel preemption latencies with the CONFIG_PREEMPT_RT mode. The test program I wrote does the following on a thread with highest priority (99) and SCHED_FIFO policy to simulate a real time thread.
t1 = gettimeofday nanosleep(for 3 ms) t2 = gettimeofday I was expecting to see the difference t2-t1 to be close to 3 ms. However, the smallest difference I see is 4 milliseconds under no system load, and the difference is as high as 25 milliseconds under moderate to heavy system load (mostly performing disk I/O). Based on the articles and the mails I read on this list, I understand that worst case latencies of 1 ms (or less) should be possible using the RT Preemption patch, but I am unable to get anything less than 4 millseconds even with sleep times smaller than 3 ms. I am running the tests on a SBC with a 1.4G Pentium M, 512M RAM, 1GB compact flash (using IDE). I believe I have the high resolution timer working correctly, because if I comment out the sleep line above t2-t1 is consistenly 0 or 1 microsecond. Following earlier discussions (in July) in this list, I tried to set kernel configuration parameters like CONFIG_LATENCY_TRACE to get tracing/debug information, but I didn't find these parameters in my .config file. I appreciate your suggestions/insights into the situation and steps that I should try to get more debug/tracing information that might help to understand the cause of high latency. Thanks for your help, sundar. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/