Re: [PATCH -v8][RFC] mutex: implement adaptive spinning

Peter Zijlstra
2009-01-12T18:07:16Z

On Mon, 2009-01-12 at 19:33 +0200, Boaz Harrosh wrote:

> Which brings me back to my initial reaction to this work. Do we need
> two flavors of Mutex? some program sections need Fairness, some need
> performance. Some need low-latency, some need absolute raw CPU power.

Thing is, its the kernel, we cannot have such knobs per task. So we have
to pick one and stick with it -- the 'best' we can do is what PREEMPT_RT
does and replace the thing whole sale at build time.

> Because at the end of the day spinning in a saturated CPU work-load
> that does not care about latency, eats away cycles that could be spent
> on computation. Think multi-threaded video processing for example.
> Thing I would like to measure is
> 1 - how many times we spin and at the end get a lock
> 2 - how many times we spin and at the end sleep.
> 3 - how many times we sleep like before.
> vs. In old case CPU spent on scheduling. Just to see if we are actually loosing
> cycles at the end.

Feel free to do so ;-)