Re: Profile the waiting time for lock or lock stats for one application

[Rodrigo Campos <rodrigo@sdfg.com.ar>]

On Mon, Mar 03, 2014 at 08:11:12AM -0800, Junjie Qian wrote:
> Hi,
> 
> Really appreciate your help on this issue!
> 1. using root solve my problem with "perf lock", thank you very much!
> 2. about the discussion on locks in user-space. I discussed this with my advisor, and found that lock contention does not mean waiting time or idle cpu-cycles sometime, for example, spin-lock in user-space that all threads/cores are still running but useless work and this cannot be detected as either system lock or idle-cpu-cycles. 

Yeah, with mutexes usually there is some spinning before waiting for the lock.

> The way, I am trying to do this, now is insert the counter into the application layer once the lock happens start the counting and I prepare to monitor the threads in queue to detect the lock.

clock_gettime() with some clocks is implemented as a VDSO, so it should be
pretty light to get that info if you need it.
And thread local variables can be very useful too probably :)

> I will let you know if I have any updates on this.

Great :)




Thanks a lot,
Rodrigo