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

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Message-ID: <20101229183016.GA455@redhat.com>
Date:	Wed, 29 Dec 2010 19:30:16 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Dario Faggioli <raistlin@...ux.it>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	torbenh <torbenh@....de>, 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 12/29, Dario Faggioli wrote:
>
> On Wed, 2010-12-29 at 14:21 +0100, Oleg Nesterov wrote:
>
> > You do not need clock_getcpuclockid() at all. In fact I do not really
> > understand what this helper should actually do, probably it is only
> > needed to validate the pid. You can simply use MAKE_THREAD_CPUCLOCK()
> > to sample a single thread via clock_gettime().
> >
> Fine, but, is that macro available for an application developer? Because
> I can find it in kernel and glibc sources, but not in my /usr/include/*,
> which is the motivation behind this attempt... But it might be my
> fault! :-P

Yes, I do not see MAKE_*_CPUCLOCK() in /usr/include.

> > IOW. Unless I missed something, with this patch, the only problem
> > is that getcpuclockid() always assumes MAKE_PROCESS_CPUCLOCK(),
> > I do not think this is the kernel problem.
> >
> Agreed, sorry for wasting (hopefully not too much) people's time. :-(

No, I think you have a point. I'd suggest you to re-send the
patch which removes this limitation from kernel side.

My only objection was, we shouldn't add the hacks to overcome
the limitations in glibc. Say, posix_cpu_clock_get() should only
check CPUCLOCK_PERTHREAD(), it should not treat !group_leader
specially just because getcpuclockid() can construct the proper
clock id. This should be solved in userland.

Oleg.

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