Re: [LTP] LTP RT Tests (Cyclic, rt-migrate, etc)

[Subrata Modak <subrata@linux.vnet.ibm.com>]

On Mon, 2009-07-20 at 10:03 -0700, Darren Hart wrote: 
> Steven Rostedt wrote:
> > On Fri, 10 Jul 2009, Darren Hart wrote:
> > 
> >> Subrata Modak wrote:
> >>> On Fri, 2009-07-10 at 22:00 +0530, Sripathi Kodi wrote:
> >>>> On Wednesday 08 July 2009 23:43:53 Subrata Modak wrote:
> >>>>> Darren/Sri/Gowri,
> >>>>>
> >>>>> Where do you want me to put this exactly inside the RT tree ?
> >>>> Hi Subrata,
> >>>>
> >>>> Going by how the tests are organized currently, I think this should go
> >>>> into it's own directory under testcases/realtime/func. We will need to
> >>>> add a makefile to it. Are you looking at us to help you with this?
> >>> Correct. Please send me a patch which integrates it into RT tests build,
> >>> install & run.
> >> Just got back from a week vacation and am burning through mail as fast as I
> >> can :-) Haven't had a look yet, but does this test use librttest.h?  I suspect
> >> not.  We'll need to adapt it to run within the existing ltp real-time testing
> >> framework, which includes things like buffered output as well as mlocking
> >> support.
> >>
> >> Lastly, I'm not sure this test does anything effectively different than
> >> prio-wake, already in the tree.  My other concerns with the test are its
> >> explicit 1ms preemption criteria (as Steven described it anyway).  We are
> >> trying to move away from criteria being inherent in measurement tests, and 1
> >> ms seems like an awfully long priority inversion to be an acceptable criteria
> >> to many users.
> >>
> >> Steven, am I missing something conceptually here?
> > 
> > Hmm, I missed this email, sorry for the late reply.
> > 
> > What does prio-wake do?
> > 
> > This test is what I used to develop the rt scheduler in mainline (as well 
> > as in -rt).  It wakes up N+1 tasks with lowering real time priorities. 
> > Where N is the number of CPUs in the system. Then it makes sure that the 
> > these tasks spread out across the CPUs. Most tests just test the highest 
> > priority task in the system. But those tests usually miss the second 
> > highest prio task in the system. If you have a second highest prio task in 
> > the system and a CPU is available to run, then it should run on that CPU. 
> > But what happens is that it can wait to be migrated and can take millisecs 
> > to wake up.
> > 
> > This test makes sure that all the high prio tasks that are in the running 
> > state are actually running on a CPU if it can.
> > 
> > Make sense?
> 
> Yup.  This is different than prio-wake.  Prio-wake creates some number 
> of threads of varying priorities and puts them to sleep on 
> pthread_cond_wait and then wakes them with pthread_cond_broadcast, then 
> tests that the threads were woken in priority order.  Fails on 
> kernels/glibc without requeue pi support as a FUTEX_WAKE(all) was used 
> for PI mutexes.
> 
> So to include this in the ltp/restcases/realtime suite, the test should 
> make use of the librttest.c and libstats.c apis, standardized argument 
> parsing, buffered logging mechanism, and standardized output formatting. 
>   I can't get to that for a little while myself, but can assist if you 
> have any questions.  Alternatively we can wait a little while, and 
> perhaps someone on my team will be able to help merge it with the 
> realtime test infrastructure in LTP.

That should be fine.

Regards--
Subrata

> 
> > 
> > (BTW, current -rt and mainline now fail this test :-? )
> 
> Hrm, uh oh.  Adding it to my lengthy list of things to try and look at :/
> 
> Thanks Steve,
> 


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