[mythtv-users] SOLVED System Load/Performance Question

[Bob Cottingham]

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.

Thanks for the info and heads up!
Bob C