Re: [Xenomai-help] 0 CPU time problem

[Tom Z <tomz30@domain.hid>]

[-- Attachment #1: Type: text/plain, Size: 2791 bytes --]

Hi Gilles,

"No, CLOCK_PROCESS_CPUTIME is a clock implemented by the Linux kernel,
so, it does not see the time spent in primary mode. If the foo function
does not suspend, you can use rt_timer_tsc(), but the answer is no,
there is currently no way to get the cpu time used when in primary mode."
Thanks a lot for the explanation. It seems my understanding on how Xenomai works was incorrect. I thought that if a task, say, myRTTask() is spawned by rt_task_create() and rt_task_start(), then myRTTask() will always run in the primary mode, so if myRTTask() calls foo(), then foo() will be running in the primary mode all the time. The correct fact is, myRTTask() could be running in either the primary mode or the secondary mode, right? This arises my another question, if foo() uses some third party libraries (with source code available), how can I tell what parts of foo() will be running in the primary mode, and what parts will be in the secondary mode? Are there principles for deciding whether the code is in the primary mode or the secondary mode?


Thanks again for your patient help.

Tom


________________________________
From: Gilles Chanteperdrix <gilles.chanteperdrix@domain.hid>
To: Tom Z <tomz30@domain.hid>
Cc: "xenomai-help@domain.hid" <xenomai@xenomai.org>
Sent: Friday, 4 November 2011 4:36 PM
Subject: Re: [Xenomai-help] 0 CPU time problem

On 11/04/2011 10:03 PM, Tom Z wrote:
> > We do not know what skin you use, we will assume that you use
> > Xenomai posix skin, so, compile with the right flags.
>
> Here is how I
> build my program, say, fooTest: gcc -I/usr/xenomai/include
> -D_GNU_SOURCE -D_REENTRANT -Wall -pipe -D__XENO__ -lnative
> -L/usr/xenomai/lib -lxenomai -lpthread -lnative -lrtdk fooTest.c -o
> fooTest

You are using the native skin then.

> > CLOCK_PROCESS_CPUTIME_ID is not implemented for xenomai posix skin,
> > so, clock_gettime probably returns an error, and the struct timespec
> > is unchanged. If somehow the glibc clock_gettime is used, and this
> > call does not cause a system call, then all bets are off, and even a
> > lockup could happen.
>
> Thanks for explaining this. So can I trust the
> CPU time I obtained with my method when the function is running in
> the primary mode? It seems you explanation implies that the results I
> obtained are not reliable, if so, are there other reliable ways to
> obtain the CPU time?

No, CLOCK_PROCESS_CPUTIME is a clock implemented by the Linux kernel,
so, it does not see the time spent in primary mode. If the foo function
does not suspend, you can use rt_timer_tsc(), but the answer is no,
there is currently no way to get the cpu time used when in primary mode.

-- 
                                                                Gilles.

[-- Attachment #2: Type: text/html, Size: 3811 bytes --]