On Tue, 15 May 2012 21:55:37 -0400 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > 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. It's called rteval and I have a git tree here: git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rteval.git It's basically some python scripting to do much of what Steven describes below. When it starts up it kicks off a kernel make with 2* the number of available processors (make -j <n*2>) and runs hackbench, both in loop. Then it kicks off cyclictest to measure the system latency under load. I usually run it like this: $ sudo rteval --duration=12h At the end it summarizes the results of the run. > > > > > 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 > >
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