Re: good load / stress suite?

[Clark Williams <williams@redhat.com>]

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On Tue, 15 May 2012 21:55:37 -0400
Steven Rostedt <rostedt@goodmis.org> 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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