Re: [RFC PATCH -rt] Priority preemption latency

[Mike Kravetz <kravetz@us.ibm.com>]

Hi Ingo,

As you can see from the note below, we are still having issues with
this testcase.  As a reminder Darren's mail with a pointer to the
new testcase is at:

http://www.uwsg.indiana.edu/hypermail/linux/kernel/0606.1/0729.html

When run with the '-i' option it fails on a regular (aprox 50% on 4 way)
basis.  Any insight into what may be happening would be appreciated.

Thanks,
-- 
Mike

On Thu, Jun 15, 2006 at 02:06:58PM -0700, 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.