[linux-audio-user] Re: x86_64 and ingo's realtime patches, works?

[Rick Wright]

Lee Revell wrote:

>On Wed, 2006-01-18 at 21:22 -0800, Mike Taht wrote:
>  
>
>>The maximum scheduling latency was 31.177 msec. Finding out
>>what caused it strikes me as an intensive exercise... and I don't
>>think anyone in their right mind would run a workload like this. 
>>    
>>
>
>It's actually not hard at all, and would be interesting to know.
>
>Just enable the latency tracing options in the kernel configuration,
>reset the tracer on boot with "echo 0
>  
>
>>/proc/sys/kernel/preempt_max_latency", and post the contents
>>    
>>
>of /proc/latency trace after generating some xruns.
>
>Lee
>
>
>  
>
Lee,

Could you elaborate a little more on which "kernel hacking" .config 
options are needed to do the latency tracing you have referred to a few 
times now?

Besides the obvious "Latency Tracing (LATENCY_TRACE)", there are others 
such as:
"Wakeup latency timing (WAKEUP_TIMING)" and it's associated histogram
"Non-preemptible critical section latency timing" 
(CRITICAL_PREEMPT_TIMING) and it's associated histogram
"Interrupts-off critical section latency timing" 
(CRITICAL_IRQSOFF_TIMING) and it's associated histogram

Each warns of increased kernel size and - more importantly - overhead 
with these options enabled.

Could you provide a brief overview of:
1) what each of these options do and used for?
2) what to expect from the "increased overhead" in practice?
3) which ones are essential to provide good latency trace feedback?

I suspect the reason many people, myself included, don't already do this 
is simply lack of knowledge.

Thanks,
Rick