[mythtv] Maybe it *is* interrupt latency

[Kyle Rose]

> I saw this with an early version of the HD3000 driver.  Have not
> seen it since v1.3, however.

On HD-3000 or 2000?  I haven't tried the 3000 card yet: it may react
better.  That's something to try.

> Does it happen with ALL of your stations?

Well, it happens at least with ABC, FOX and PBS-HD.  Haven't tried the
others, but ABC and PBS-HD have very high signal strength (>90%) and
FOX has sufficient signal (>75%).

> What kernel are you running?  I have custom configured 2.6.7 and
> 2.6.9 kernels.  The 2.6.7 kernel works better.  That may be because
> I have "pci=noapic" for the 2.6.7 kernel, and not for the 2.6.9
> kernel, however.

I am using 2.6.9 with noapic nolapic (seems this behavior isn't quite
as bad with APIC support off) and with acpi on (some things, notably
on-board USB, seem not to work with acpi off).

> Jack (at pcHDTV.com) suggested turning *off* preemptive scheduling,
> which I have done in both.

I had CONFIG_PREEMPT off initially; didn't notice much difference when
I turned it on, so maybe I'll shut it off again.

Given how intermittently this happens (once every few seconds) I think
I'm right on the cusp of being able to handle it with the current
system.  Would suck to have to get a faster processor just to mitigate
high interrupt latencies when an 1800+ is overkill for the work this
machine needs to do 99% of the time.

Cheers,
Kyle