[linux-audio-user] my usb audio experience with 2.6.8.1 and 2.6.11 & ingo molnar's patches

[Ryan Gallagher]

The Hardware:			The software:

Dell inspiron 5100		Gentoo ~x86
P4 2.4				kernel 2.6.8.1 ingo molnar's VP patch 09
640mb ram			kernel 2.6.11-rc4 ingo molnar's RT patch
40gb 7200rpm			jackd version 0.99.50
ati radeon m9			alsa lib/drivers 1.0.8
edirol ua-25 USB interface	FS filesystem


The problem/experience:

I'm able to get good low latency performance from kernel 2.6.8.1 ingo
molnar's VP patch 09 as described
http://www.affenbande.org/~tapas/wiki/index.php?USB%20Low%20Latency%
20Success but with 2.6.11-rcX I'm unable to get any kind of decent low
latency performance.  Tons of "subgraph timeouts" and "delay of X usecs
exceeds..." plus lots of XRUNS.  Making the usb IRQs unthreaded in
2.6.11-RT has no effect.  At -p 1024 -n 2 jackd runs pretty well, but
there's no way I can touch -p 124 -n 3 that I get with 2.6.8.1-VP.

The Question:

Has ANYONE had success with 2.6.11 and low latency USB?  I don't want to
keep bashing my head against this if it's just "not ready yet".

Also a quick tip:

Many of my devices were piled up on IRQ11 (I realize this is not the
horrible issue it once was) and I could find no way of getting things
moved around (it's a laptop so no card shuffling) and went through a TON
of kernel boot options to no effect... till I found acpi_irq_balance.

I went from this:
 11:    3376988          XT-PIC  uhci_hcd, uhci_hcd, uhci_hcd, ehci_hcd,
ohci1394, radeon at pci:0000:01:00.0  0/76988

To this:

  9:     245868          XT-PIC  acpi, radeon at pci:0000:01:00.0
 10:    2092423          XT-PIC  uhci_hcd, ehci_hcd
 11:    1363802          XT-PIC  uhci_hcd, uhci_hcd, ath0, ohci1394

Maybe it's a psychological effect but low-latency audio seems a bit more
stable now.

BTW, I recommend the edirol UA-25 to anyone looking for USB with phantom
power, mic pres and midi.  (as with any USB device, be prepared to tweak
to get performance).

Thanks all,
-ry
-- 
Ryan Gallagher <ruinaudio at comcast.net>