linux-kernel - Re: linux missing support for _POSIX_THREAD

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Message-Id: <20090527174954.085AAFC36B@magilla.sf.frob.com>
Date:	Wed, 27 May 2009 10:49:53 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Chris Friesen <cfriesen@...tel.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Ulrich Drepper <drepper@...hat.com>
Subject: Re: linux missing support for _POSIX_THREAD_CPUTIME?

> POSIX defines optional support for clock ID values obtained by invoking
> pthread_getcpuclockid().  When passed to clock_gettime(), this allows
> the caller to request the CPU-time clock of an arbitrary thread within
> the same process as the caller.
> 
> It appears that linux doesn't support this functionality--is that
> correct?  Is there any plan to enable this?

glibc does implement pthread_getcpuclockid using the kernel support for it.
It uses MAKE_THREAD_CPUCLOCK(tid, CPUCLOCK_SCHED) (see linux/posix-timers.h).

> Is there any current way to obtain the runtime of a particular thread
> without knowing its tid (since the thread_id to tid mapping is known
> only to glibc)?

You need a tid to construct the clock ID with MAKE_THREAD_CPUCLOCK().
The pthread_getcpuclockid function exists to do this for you when you are
using pthreads.  If you are not using pthreads, then certainly you have to
figure out what a thread's tid is yourself.


Thanks,
Roland
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