Re: [RFC PATCH -rt] Priority preemption latency

[Darren Hart <dvhltc@us.ibm.com>]

On Thursday 15 June 2006 14:06, Mike Kravetz wrote:
> On Mon, Jun 12, 2006 at 08:38:24AM -0700, Darren Hart wrote:
> > I started running this version of the patch with prio-preemt in a loop
> > over 10 hours ago, and it's still running.  This seems to be the right
> > fix.
>
> Unfortunately, this test did eventually fail over in our environment.
> John Stultz added the concept of 'interrupter threads' to the testcase.
> These high priority RT interrupter threads, occasionally wake up and
> run for a short period of time.  Since these new threads are higher
> priority than any other, they theoretically should not impact the
> testcase.  This is because the primary purpose of the testcase is to
> ensure that lower priority tasks do not run while higher priority tasks
> are waiting for a CPU.
>
> After adding these interrupter threads, the tetscase fails (on a system
> here) about 50% of the time.  An updated version of prio-preempt.c is
> attached.  It needs the same headers/makefile/etc as originally provided
> by Darren.

Thanks for the update Mike!  I have incorporated the interrupter threads using 
a command line argument, -i, they are disabled by default.  Grab the latest 
here:

http://linux.dvhart.com/tests/

To run the test on a 4 way machine with interrupter threads enabled, use:

$ ./prio-preempt -n 4 -i

>
> Any help figuring out what is happening here would be appreciated.

-- 
Darren Hart
IBM Linux Technology Center
Realtime Linux Team
Phone: 503 578 3185
  T/L: 775 3185
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