[mythtv-users] System Load/Performance Question

[Brian Wood]

On Feb 20, 2006, at 9:37 AM, yan seiner wrote:

> Brian Wood wrote:
>
>> On Feb 19, 2006, at 10:00 PM, Brian Wood wrote:
>>
>>
>>
>>> 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..
>>>>
>>>>
>>>>
>>> OK, I'll do that, thanks.
>>>
>>> I should have mentioned BTW, I am getting "prebuffering pauses" from
>>> the frontend when these glitches happen.
>>>
>>>
>>
>> Also: I've always got a message when ivtv inits:
>>
>> "Unreasonably low latency timer setting to 64 (was 32)"
>>
>> I'd always ignored this because I'd seen it in a lot of posted logs,
>> so I more or less assumed it was normal.
>>
>>
> The way I understand PCI latency, the greater the number, the more  
> time
> slices that slot gets.  So you can increase bandwith by increasing
> latency, by 'buffering' those transfers on the card.  So you can play
> with latencies to give some cards more ability to transfer data.  Too
> short latencies drive overhead to the point where data transfers are
> very slow.

That's my understanding as well. For example my video card is set to  
248, which is the max. My PVR cards are set to 64, ethernet is set to  
32. The host bridge itself is set to 8. Comparing to other systems  
I've checked these seem to be reasonable values. The IDE interface is  
set to 32, which might be on the low side. They can be set easily  
with the 'setpci" command, I've not found a way to set them via my BIOS.

>
> You can do this in the bios for some machines but also via /proc; I
> think linux sets PCI latencies so I'm not sure how the BIOS and linux
> settings work.


One question I've come up with: according to hdparm all my drives are  
using DMA, but 'cat/proc/dma' shows only "4: cascade". This is also  
the case for every other system I've checked so I'm not too  
concerned, but I do wonder why this might be.