[mythtv] Maybe it *is* interrupt latency

John Patrick Poet john at BlueSkyTours.com
Mon Jan 10 15:44:35 EST 2005



On Mon, 10 Jan 2005, Kyle Rose wrote:

> So I think I had it backwards: the pcHDTV driver seems to report
> buffer overrun when the device read buffer fills up because the
> application isn't reading fast enough.  This is probably therefore not
> the issue.
>
> I did a test today outside of myth with dtvstream and dd.  I set up
> dd's from /dev/video1 and /dev/video3 (the two PVR cards) to some file
> on the NFS recordings partition, and then started a dtvstream to a
> file on the same partition, which somewhat emulates the behavior of
> mythtv but allows me finer-grained control over what happens when.
>
> Well, even when running dtvstream with fifo priority, I still get
> sync-loss messages intermittently:
>
> Lost sync at input offset 8467669
> Achieved sync after 188 bytes.
> Lost sync at input offset 12109605
> Achieved sync after 188 bytes.
> Lost sync at input offset 13320325
> Achieved sync after 72 bytes.
> Lost sync at input offset 13369465
> Achieved sync after 116 bytes.
> Lost sync at input offset 15749473
> Achieved sync after 188 bytes.
> Lost sync at input offset 16711484
> Achieved sync after 188 bytes.
> Lost sync at input offset 26417172
> Achieved sync after 188 bytes.
> Lost sync at input offset 54481624
> Achieved sync after 564 bytes.
>
> which suggests the driver is losing part of a packet or several
> packets because the first byte it encounters isn't the SYNC_BYTE.
>
> Anyone seen this before?  Not clear whether anything short of (a) a
> faster process or (b) IRQ threads will solve this problem, and I don't
> know if (b) is stable enough for me to want to try again.
>
> Cheers,
> Kyle
>

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

Does it happen with ALL of your stations?

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.

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

John


More information about the mythtv-dev mailing list