[mythtv-users] DVB(S) tuner sensitivity (and my other) experiences

[Robert]

Dave wrote:
> Possible one of two things.
> 
> 1. Your disk is taking all the interrupts whilst recording and your 
> not getting anything for your dvb or vide card. Try unmasking
> interrupts for your disk, or shuffle your interrupts as described.

I don't think it is a disk problem, because when I used the nv driver
for a short trial everything working ok.  Plus I have unmaskirq = 1 set
for my disk.


> 2. Or, likely your 'nvidia' driver is sharing interrupts with some
> other critical hardware and the 'nv' driver isn't. I believe the
> nvidia quadro cards are woefully inadequate and supported only by
> legacy nvidia drivers ?

Unfortunately the Nvidia driver is using the same interrupt as the
HVR3000 card (cx88).  I've tried changing settings in the bios to swap
the interrupts around, and managed to get them to be different, but it
didn't help with the problem.  I've also tried changing the pci
latencies, using setpci, but that didn't make any difference either.

I've not tried noapic or irqpoll though, so maybe I will give those a
try and see if it helps.

Swapping slots isn't an option as both PCI slots are used and the 
graphics card is AGP.  And yes, the Quadro is only supported by the 
legacy NVidia drivers, but the version number isn't that far behind the 
latest drivers.  (The card was given to me which is why I'm using it!)


> 
> Have you looked at vmstat to see your cpu/interrupt usage ?

I have, CPU usage is generally low (10%) when recording DVB-S and 
doesn't max out at any point.

How do you check interrupt usage with vmstat?  Is this just the IO column?

Robert.

mythbox ~ # hdparm /dev/hda |grep unmask
  unmaskirq    =  1 (on)

mythbox ~ # cat /proc/interrupts
            CPU0
   0:   58180140    IO-APIC-edge  timer
   8:          2    IO-APIC-edge  rtc
   9:          0   IO-APIC-level  acpi
  14:     248445    IO-APIC-edge  ide0
  15:        128    IO-APIC-edge  ide1
  16:   10214394   IO-APIC-level  uhci_hcd:usb3, cx88[0], cx88[0],
cx88[0], nvidia
  17:    4697686   IO-APIC-level  uhci_hcd:usb1, Bt87x audio, bttv0
  18:       1210   IO-APIC-level  uhci_hcd:usb2
  19:        104   IO-APIC-level  ehci_hcd:usb4
  20:     152190   IO-APIC-level  Intel ICH5
  21:     180893   IO-APIC-level  eth0
NMI:          0
LOC:   58181682
ERR:          0
MIS:          0