[mythtv-users] SOLVED System Load/Performance Question

[Brian Wood]

On Feb 20, 2006, at 4:08 PM, Bob Cottingham wrote:

> On 2/20/06, Brian Wood <beww at beww.org> wrote:
>> On Feb 19, 2006, at 9:57 PM, Yan Seiner wrote:
>>> Brian Wood wrote:
>>>> 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
>>
>> 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.
>
> This sounded like it could be related to problems I've been seeing
> with ivtv corruption and prebuffering pauses, however with my nforce2
> chipset I can't adjust the pci latency for the IDE, audio or a few
> other controllers, which are all set to 0.  I don't have a problem
> changing the latency for the build-in video (which was set to 248) and
> the ivtv cards.  I found this to be the case for both nforce2 based
> systems I tried.  I didn't find anything through google that really
> addressed this issue.  Does anyone else see this?  Is this a potential
> issue?  Is there any reason to have the video card latency so high?  I
> lowered the video latency and I'm going to see what effect it has on
> performance.
>
I didn't set any latencies in BIOS, couldn't find any way to do that  
if I wanted to.

I used 'setpci' to do it after the system had booted. I'll have to  
set it up to do that automatically, something like rc.local.

All of my systems have the graphics card (AGP) set to 248, and I  
would think that is required to get the max performance from the  
graphics card.

My amd64 with a VIA chipset had the IDE latency set to 32, while  
another of my machines (Intel Tehema chipset) had it set to 0, not  
sure what's going on there since I have so few datapoints. Increasing  
that 0 might have unexpected results, but increasing the ide/sata  
latency from 32 to 176 seems to have solved my problem.

I'm going to enter something in the wiki about this, but I want to  
research and experiment a bit more so I will (hopefully) not mis-lead  
anyone.