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

[Pieter Palmers]

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.

>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.

Pieter