[ltt-dev] trace a futex

[compudj@krystal.dyndns.org (Mathieu Desnoyers)]

* Gian Lorenzo Meocci (glmeocci at gmail.com) wrote:
> Hi Mathieu,
> 
> thanks for your reply.
> 
> I want specify that:
> 1) I am already patching glibc (and, of course, nptl/pthread_*)
> 2) I already add two event to pthread_mutex_lock. The first at the
> beginning of the function and the second after all return 0 presented
> on that function. But those two events are not enough to establish if
> a pthread_mutex_lock has been blocking.
> In fact I know only the time spent on pthread_mutex_lock. If this time
> is little probably I hold the mutex otherwise I was been descheduled.
> 
> So thanks a lot again,
> 
> 

Ok, then you will probably want to correlate your information with :

- scheduling activity regarding your threads
- system call entry events, especially sys_futex. Note that a thread
  calling sys_futex won't _necessarily_ be put to sleep.. it may still
  be able to take the lock relatively quickly.

If you need more than that, we may think of instrumenting futex.c, but I
am not sure this is required.

Mathieu

> -- 
> Ing. Gian Lorenzo Meocci
> http://www.meocci.it
> 

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68