On Tue, 2012-05-15 at 16:08 -0700, Matthieu Bec wrote: > Hello all, > > I was wondering what people used to check RT_PREEMPT behavior under > load/stress? There is a test suite that Red Hat uses called rt-eval (I believe). Clark can give you more info on that. > > I'm trying to test the accuracy of my timers and have a test where I > setup a kernel module with an hr-timer flipping RTS bit on serial COM0 > periodically, which I can look on an oscilloscope. the scope triggers on > rising edge, I call jitter what shows on the falling side: > under no specific load I get ~ 10 us (worst case waiting a long time) > > > My initial idea for stressing the system was to compile a kernel, make > -j 8 (#cores) that I thought would exercise CPU and IO if anything. As > it happens, it's "mostly good" but I do get occasional (but repeatable) > wild excursions (>100us) The tests I do is the following: I run "cyclictest -n -p 80 -t -i 250" then in another window I run a kernel compile using distcc (to stress the network as well) with make -j40, it basically does: while :; make clean; make -j40; done Then I also run hackbench (written by Rusty Russell), with: while :; hackbench 50 ; done I run the above on a single machine, while on another machine I run ktest against the -rt kernel to test different configs (with and without PREEMPT_RT enabled and such). I do this for both i386 and x86_64. > > Looking around, I found a tool called 'stress' - > http://weather.ou.edu/~apw/projects/stress/ > Under these new conditions, the system behaves really well again ~20 us > stable all the way. > > So both tests give different result, I'm not sure which to trust. > I was thinking maybe there is some weird interaction with the kernel and > building the kernel that make the 'bad' test invalid? > > I have RT_PREEMPT 3.0.18-rt34 SMP x86_64 > Now, I run the above stress tests that I mentioned for several hours before I release a stable kernel. I run this on a 2.6GHz xeon core2, and I may hit at most 70us latency with cyclictest. That's a high, it usually stays below 50us. We consider >100us on this type of hardware a bug which needs to be fixed. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
