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

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

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.

> 
> (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,

-- 
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team

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