Messages in this thread | | | Subject | Re: [PATCH resend] Reading POSIX CPU timer from outside the process. | From | Dario Faggioli <> | Date | Wed, 29 Dec 2010 15:10:14 +0100 |
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On Wed, 2010-12-29 at 14:21 +0100, Oleg Nesterov wrote: > > > How so? For example, with this change > > > clock_getres(MAKE_THREAD_CPUCLOCK(pid_of_sub_thread)) won't work, no? > > > > > I tested all the clock_getres() calls that came to my mind (at least the > > one that are possible from an userspace program), and they always worked > > because of this (still in check_clock): > > > > const pid_t pid = CPUCLOCK_PID(which_clock); > > > > if (pid == 0) > > return 0; > > > > Which triggers all the times, > > No, please note pid_of_sub_thread above. > Sure, I saw that... I was referring to all the clock_getres() and clock_{get,set}time() I was able to call without using directly MAKE_THREAD_CPUCLOCK.
> > Which won't work because CPUCLOCK_PERTHREAD(which_clock) is always false > > in this case. > > I guess, this is because glibc passes MAKE_PROCESS_CLOCK() id, right? > But we shouldn't add the hacks to the kernel to hide the limitations > in glibc. > Exactly. Actually, I didn't noticed this too when I first started with this patch, and the fact that my first version worked -- which was by chance, I can say it now :-P -- made me think it was worthwhile to bend the semantic a bit, to enable this new capability... But making it work is hackish, I see it now. Sorry. :-)
> BTW. What is the test-case? I am looking at http://gitorious.org/clockid, > I guess it is clockid.c... > Yep. A very trivial one, I agree, but it's just to show the issue.
> 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
> 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. :-(
Thanks and 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@jabber.org [unhandled content-type:application/pgp-signature] | |