Re: [Fwd: Re: [patch] Real-Time Preemption, -RT-2.6.9-mm1-V0.4]

Ingo Molnar
2004-11-01T14:06:21Z

* Ingo Molnar <mingo@elte.hu> wrote:

> > removing the poll() lines doesnt seem to impact the quality of the
> > data, but i still see roughly 50 usecs added to the 'real' latency
> > that i see in traces.
>
> this i think is related to what Thomas observed, that there's a new
> irqs-off critical section somewhere. (it's in the new priority
> handling code i think.)

ah, found it. Only RT tasks were supposed to get special priority
handling, while in fact all tasks got it - so when Thomas ran hackbench
(Thomas, you did, right?) it created an O(nr_hackbench) overhead within
the mutex code ... I've uploaded -V0.6.5 to the usual place:

http://redhat.com/~mingo/realtime-preempt/

Thomas, can you confirm that this kernel fixes the irqs-off latencies?
(the priority loop indeed was done with irqs turned off.)

i'm not sure this fix is related to the deadlocks reported though.

Ingo