linux-kernel - Re: [PATCH resend] Reading POSIX CPU timer from outside the process.

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Date:	Tue, 04 Jan 2011 12:01:25 +0100
From:	Dario Faggioli <raistlin@...ux.it>
To:	torbenh <torbenh@....de>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	john.stultz@...aro.org, roland@...hat.com,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Stanislaw Gruszka <sgruszka@...hat.com>,
	Dhaval Giani <dhaval.giani@...il.com>,
	Randy Dunlap <rdunlap@...otime.net>
Subject: Re: [PATCH resend] Reading POSIX CPU timer from outside the
 process.

On Thu, 2010-12-30 at 18:45 +0100, torbenh wrote: 
> > I think we should change glibc if clock_getcpuclockid() doesn't work,
> > please see below.
> 
> http://www.kernel.org/doc/man-pages/online/pages/man3/pthread_getcpuclockid.3.html
> 
> this one works.
> ok... it takes a pthread_t for identifying the thread.
> but it works.
> 
Well, I knew this, I knew it very well, as you can see from the code on
the git I pointed to (it's part of one of the examples!).

the thing is that I believe there are situations where it could be
useful to sample CLOCK_THREAD_CPUTIME_ID from a _different_ process, and
in that case, you can't access that thread's pthread-id, can you? :-O

The jack2 code I saw could be one of these "potential user", and AFAICT
your jack1 might be another one, no?
Yeah, I know, whether you can/want use this or not also depends on other
issues, but you are in a _different_ process --and thus you can't use
pthread_* calls-- aren't you?

I'm now looking at Oleg's solution and into glibc as well... I'll come
out with something ASAP.

Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
----------------------------------------------------------------------
Dario Faggioli, ReTiS Lab, Scuola Superiore Sant'Anna, Pisa  (Italy)

http://retis.sssup.it/people/faggioli -- dario.faggioli@...ber.org

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