Fwd: Help with debugging a POSIX timing test.
Chirayu Desai
chirayudesai1 at gmail.com
Tue Nov 26 03:49:27 UTC 2013
On 26 November 2013 00:40, Joel Sherrill <joel.sherrill at oarcorp.com> wrote:
> On 11/25/2013 10:58 AM, Chirayu Desai wrote:
> >
> > Sorry, I sent the last message to only Joel.
>
> I MIGHT have eventually gotten to it. But am swamped.
>
> > ---------- Forwarded message ----------
> > From: *Chirayu Desai* <chirayudesai1 at gmail.com
> > <mailto:chirayudesai1 at gmail.com>>
> > Date: 25 November 2013 15:30
> > Subject: Re: Help with debugging a POSIX timing test.
> > To: Joel Sherrill <joel.sherrill at oarcorp.com
> > <mailto:joel.sherrill at oarcorp.com>>
> >
> >
> >
> >
> >
> > On 25 November 2013 00:35, Joel Sherrill <joel.sherrill at oarcorp.com
> > <mailto:joel.sherrill at oarcorp.com>> wrote:
> >
> > Now that I can see and run the code, a few things
> > jump out.
> >
> > + POSIX priorities -- lower numerically ==> more important
> > + You did &Thread_Id to calls after created. The & isn't
> > supposed to be there.
> >
> > + &policy should be the second argument to
> > pthread_getschedparam.
> >
> > This explains the ESRCH I was getting.
>
> Yep. And one of the compiler warnings as well. :)
>
> > + Pay attention to compiler warnings. :)
> >
> > Sorry for not doing so.
>
> No problem. This is a good example of how properly addressing
> the warning would have fixed the issue with no time in the
> debugger. Good programming practices try to keep you out of
> a debugger. :)
>
> > + Benchmark time is initialized IMMEDIATELY BEFORE the
> > single operation under test. We try to avoid including
> > anything.
> >
> > Got it.
> >
> >
> > I have attached a new version of init.c with comments
> > hacked in and changes.
> >
> > Thanks.
> >
> >
> > The big thing I tried to put in a comment block is that
> > the way this test is structured, it includes the hidden
> > start up time for the first time test_thread(0 runs.
> > I tried to write up notes on how to modify the test
> > to avoid that.
> >
> > I was unable to understand all of it.
> > From what I understood, POSIX_Init is called first, which
> > cals benchmark_pthread_setschedparam.
> > That creates a new thread, gets the priority and policy, and then
> > setschedparam is called
> > with the new (lowered) priority, which is what we want to test.
>
> pthread_create() creates and starts the thread. If it is
> more important than POSIX_Init(), it will immediately be
> switched to and run. But it isn't so it won't run until
> POSIX_Init() lowers its priority.
>
That makes it much more clear.
>
>
> > For convenience, I would add a helper routine like
> > this:
> >
> > void set_thread_priority( id, new_priority )
> >
> > and call it. It will greatly simplify the code.
> >
> > Noted, I will do that after I get a better understanding of the code.
>
> Since you will be changing priority multiple times to switch
> back and forth, this will really help tighten the code.
>
Done [0] :)
>
>
> > I hope I didn't fall into the inverse
> > priority range trap in those instructions....
> >
> > WARNING: POSIX priorities run INVERSE from the internal
> > priorities but in gdb if you print:
> >
> > p _Per_CPU_Information.per_cpu.executing->current_priority
> >
> > You will see the internal priority (NOT POSIX priority)
> > of the currently running thread. 1 is most important
> > and 255 is the IDLE task.
> >
> > I'm confused.
> > Per
> http://www.rtems.org/onlinedocs/doxygen/cpukit/html/group__POSIX__PRIORITY.html#gada0c9a015d42fd545af7454f1ca0d098
> ,
> > "RTEMS Core has priorities run in the opposite sense of the POSIX API."
> > So, for this task, lowering the POSIX priority is what we want, it is
> > the output I'm getting which confuses me
> >
> > Original priority: 2
> > Lowered priority: 4
>
> I am going to do this as a mix of internal and
> POSIX priorities
>
> Internal 255 is the lowest priority and illegal in POSIX.
> Internal 253 = POSIX_Init() at start (POSIX 2)
> see cpukit/posix/src/pthread.c for the default attributes
>
> Where you say lowered, it is actually becoming more important
> and moving to a numeric value with numbers above and below.
> At 2, there is little room below it. It is the next to lowest
> POSIX priority value.
>
> test_thread() is created at priority 2 also because the
> attributes are NULL.
>
> What you print as "Lowered priority" is actually the priority
> of test_thread() if I am reading things correctly.
>
> Hint: Make your set priority helper take (const char *, id, priority)
> and you can print the thread name in debug messages. :)
>
> When I break at test_thread(), the priority is POSIX=4, Internal=251
>
> I'm getting the hang of this now.
>
> > So the numbers you pick are important to switch back and
> > forth between the tasks.
> >
> > I think the test is pretty close in spite of all that I
> > wrong. I stepped through the code attached and it is
> > doing the right thing EXCEPT including the thread hidden
> > start time. :)
> >
> > Benchmark programs are hard to get right but fun to write.
> >
> > Indeed
>
> :)
>
> Hope this helps.
>
> Stepping in gdb and printing the priority of the current thread
> helps. It will be the internal priority though.
>
> b POSIX_Init
> b test_thread
>
> and use
>
> p _Per_CPU_Information.per_cpu.executing->current_priority
>
> Using breakpoints did help, thanks.
I have attached a new patch, and cross-posted it to melange as well.
>
> >
> > --joel
> >
> > On 11/24/2013 11:50 AM, Joel Sherrill wrote:
> > > Sorry to be lazy/stupid but how to I download just
> > > the diff to see what's going on? I am not that
> > > github literate.
> > >
> > > --joel
> > >
> > > On 11/24/2013 11:28 AM, Chirayu Desai wrote:
> > >> Hello everyone.
> > >>
> > >> I am Chirayu Desai, a high school student, currently
> participating in
> > >> Google Code-In 2013
> > >>
> > >> I have currently working on the task [0], but I'm having some
> trouble
> > >> trying to get my code[1] to work.
> > >>
> > >> The task is to create a POSIX timing test psxtmthread05.
> > >> The test case is: pthread_setschedparam() - lower own priority.
> > >> I managed to write up something [2], but it doesn't work.
> > >> The GDB output is:
> > >>
> > >> (gdb) r
> > >> Starting program:
> > >>
> >
> /home/cdesai/rtems/b-sis/sparc-rtems4.11/c/sis/testsuites/psxtmtests/psxtmthread05/psxtmthread05.exe
> > >>
> > >>
> > >> *** POSIX TIME TEST PSXTMTHREAD05 ***
> > >> getschedparam: 3
> > >> Original priority: 5
> > >> Lowered priority: 4
> > >> setschedparam: 3
> > >> pthread_setschedparam - lower own priority 2226
> > >> *** END OF POSIX TIME TEST PSXTMTHREAD05 ***
> > >> [Inferior 1 (process 42000) exited normally]
> > >>
> > >> [0]:
> > >>
> >
> http://www.google-melange.com/gci/task/view/google/gci2013/6383096106582016
> > >> [1]: https://github.com/chirayudesai/rtems/tree/psxtmthread05
> > >> [2]:
> >
> https://github.com/chirayudesai/rtems/commit/890cebf084ca2a3815e3049a766276ddcdb0188a
> > >>
> > >> P.S. This is my first post to this list, so excuse me for any
> > mistakes.
> > >>
> > >> Regards,
> > >> Chirayu Desai
> > >
> > >
> > >
> >
> >
> >
> > --
> > Joel Sherrill, Ph.D. Director of Research & Development
> > joel.sherrill at OARcorp.com On-Line Applications Research
> > Ask me about RTEMS: a free RTOS Huntsville AL 35805
> > Support Available (256) 722-9985
> >
> >
> >
>
>
>
> --
> Joel Sherrill, Ph.D. Director of Research & Development
> joel.sherrill at OARcorp.com On-Line Applications Research
> Ask me about RTEMS: a free RTOS Huntsville AL 35805
> Support Available (256) 722-9985
>
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