[linux-audio-dev] Re: [Freebob-devel] [REQUEST] test the influence of linux1394 kernel drivers on scheduling latency

[Lee Revell]

On Fri, 2006-06-23 at 12:12 +0200, Pieter Palmers wrote:
> Lee Revell wrote:
> 
> >On Fri, 2006-06-23 at 09:44 +0930, Jonathan Woithe wrote:
> >  
> >
> >>Despite what the log says, this was running a 2.0 GHz "Dothan"
> >>Centrino CPU. Kernel was 2.6.16-rt25, distro was Slackware 10.2.  Both
> >>the stress tester and the monitor were run with RT privilege access.
> >>The firewire interface used has a TI OHCI chipset.
> >>
> >>I apologise that the run was particularly short and that therefore the
> >>statistics aren't particularly good, but it does seem to confirm the
> >>observations you made on your machine.  The large latencies only occur
> >>when the stress tester is running. 
> >>    
> >>
> >
> >What if you run the latency tester at RT priority 99?  Testing at 80 is
> >not particularly useful.
> >  
> >
> Why not?
> 
> If the 1394 test user thread has a lower priority, and the ohci1394 irq 
> priority is also lower, there is no reason for the latency tester to be 
> preempted by them.
> 

Because as you stated below the system timer runs at a higher priority
by default.  I wanted to rule out preemption by the system timer thread.

> >If anything else is running at 99, what happens if you lower those other
> >processes to 98?
> >  
> >
> I'll have to recheck, but if I remember correcly I have done this 
> experiment. The only thing at 99 is the system timer. I tried giving it 
> a lower priority than the latency test thread, which didn't change anything.
> 

OK thanks, that answers my question.

> Pieter
>