Re: [PATCH 4/4] Implement semaphore latency tracer

Peter Zijlstra
2008-10-12T19:13:28Z

On Sun, 2008-10-12 at 16:12 +0300, Török Edwin wrote:
> Each time a down_read or down_write fails, a unique latency id is generated.
> Later when someone releases the semaphore, it is blamed for the latency of all
> tasks on the wait_list of the semaphore.
> If you would group the output from latency_trace by the latency_id you get all those
> who were contending on a lock, and the tasks that were holding the lock.
> An entry in latency_trace has the format:
> (latency_id) [semaphore_id] read|write
> stacktrace <= stacktrace

What can this tracer do that latencytop cannot already do?