[mythtv] Maybe it *is* interrupt latency

[Kyle Rose]

>  DFI PRO875B motherboard
>  3.0 GHz HT P4 cpu
>  1GB RAM
>  Three HD-3000 cards
>  Fedora Core 2 with stock 2.6.7 kernel (custom configured)
>  Myth CVS as of Jan 8th.
>
> I can record three shows simultaneously, while watching a fourth, with
> absolutely no data loss or coruption.

Well, at least I know it's possible; it could just be that the HD-2000
is inferior to the 3000.  I'll try the 3000 tonight.

> If you think it is a PCI latency issue, search the Myth users archive for
> subject "PCI/AGP Latency".

I don't think it is a PCI latency issue: I doubt the bus is even 20%
busy, so the chances of there being significant contention causing
latency is pretty low.  I think it's software latency in the kernel:
something in the kernel is consuming CPU time in such a way that the
bttv driver is being starved just enough to cause it to intermittently
lose data from the hardware buffer.

Is there an easy way to tweak the timeslices given to individual
processes?  If I shorten the timeslice, I'll use more CPU in overhead,
but the kernel may circle around to the bttv driver more often,
reducing the potential for lost data.  Not sure how to do this since,
oh, sometime in the linux 1.3.x days. :)  It's just something to try,
I guess.

Cheers,
Kyle