[mythtv-users] SOLVED System Load/Performance Question

[Brian Wood]

On Feb 19, 2006, at 9:57 PM, Yan Seiner wrote:

> Brian Wood wrote:
>
>> I don't see any problems there (the cx88 card is not set up in
>> MythTV), the only sharing I see is USB, which I'm not using.
>>
>> I just set up the offending situation again to get these numbers and
>> I'm again getting the digital breakup, and occasional audio hits.
>> vmstat shows 97 % idle and 0 wa. Mythfrontend shows between 12 and 15
>> % CPU
>>
>>
> Google for PCI latency....  That may give you some relief, or not.
>
> ISTR you can adjust it via /proc..
>
> --Yan


Wow, Yan, you get the "Helpful Soul" award of the Month, if not the  
year !!!

I get to learn something new *and* fix my problem.

I never paid any particular attention to PCI latency, never had a  
reason to, until now, I suspect most folks are in the same boat.

Apparently the VIA BIOS simply sets all latencies to 32, except for  
the bridges etc. Some things can intervene and set a value to  
something else, the ivtv modules and the nVidia module for example.

Since IVTV had set the latencies of the PVRs to 64, and my IDE bus  
was still at 32, The effective bandwidth of the two PVR cards  
combined was significantly greater than the IDE system.

Adjusting the IDE latency to 176 (b0 hex) seems to have solved the  
problem. I have been watching live TV with a recording happening  
along with a comm flag job for over an hour now with no glitches and  
no pre-buffering messages.

I checked my Dell box, which has an intel "Tehema" PCI controller,  
and it seems to set everything to 64, except for some reason it sets  
the IDE latency to 0, which seems weird but it might be tied in to  
the IDE controller's function somehow. IVTV accepts this and does not  
complain, as it does about the 32 value on the VIA-based machine.

One lesson here is to never ignore a warning in the boot messages,  
like the one from ivtv about latency.  I will study the matter more  
as I suspect all latencies can be optimized to improve overall system  
performance (network, sound etc.). Setting them all to some default  
seems like the easy way out for the manufacturers.

Thanks again, and hopefully this thread being in the archives will  
help somebody else sometime. I wonder how many other "odd" problems  
are related to this.