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From: Roland McGrath <roland@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
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Cc: Chris Friesen <cfriesen@nortel.com>, LKML <linux-kernel@vger.kernel.org>,
       Ulrich Drepper <drepper@redhat.com>
Subject: Re: linux missing support for _POSIX_THREAD_CPUTIME?
In-Reply-To: Thomas Gleixner's message of  Wednesday, 27 May 2009 18:56:15 +0200 <alpine.LFD.2.00.0905271855290.3397@localhost.localdomain>
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X-Zippy-Says: Is this TERMINAL fun?
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Date: Wed, 27 May 2009 10:49:53 -0700 (PDT)
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> 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