Re: [patch 00/15] Generic Mutex Subsystem

[Ingo Molnar]

* Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> > The numbers make me suspect that Ingo's mutexes are unfair too, but I've
> > not looked at the code yet.
> 
> Yes, Ingo's code does act like this unfairness.  Interesting also is 
> that Ingo's original code for his rt_mutexes was fair, and it killed 
> performance for high priority processes.  I introduced a "lock 
> stealing" algorithm that would check if the process trying to grab the 
> lock again was a higher priority then the one about to get it, and if 
> it was, it would "steal" the lock from it unfairly as you said.

yes, it's unfair - but stock semaphores are unfair too, so what i've 
measured is still a fair comparison of the two implementations.

lock stealing i've eliminated from this patch-queue, and i've moved the 
point of acquire to after the schedule(). (lock-stealing is only 
relevant for PI, where we always need to associate an owner with the 
lock, hence we pass ownership at the point of release.)

> Now, you are forgetting about PREEMPT.  Yes, on multiple CPUs, and 
> that is what Ingo is testing, to wait for the other CPU to schedule in 
> and run is probably not as bad as with PREEMPTION. (Ingo, did you have 
> preemption on in these tests?). [...]

no, CONFIG_PREEMPT was disabled in every test result i posted. (but i 
get similar results even with it enabled.)

	Ingo
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