linuxaudio.org

On 05/01/12 20:32, Fernando Lopez-Lezcano wrote:

quoted text
> (I don't seem to find the start of the thread in my mailbox)

>

> ohci_hcd is there is you specify usb in the list of priorities rtirq

> needs to raise. And nvidia is there probably because it shares an

> interrupt with a real soundcard. Rtirq does not raise the priority of

> only the soundcard, but everything that uses the interrupt that the

> soundcard uses.

>

Afaik this is not true. The threadirqs kernel option (or a real-time

kernel) creates bottom halves (or tasklets, or softirqs) of each device

that has or shares an IRQ. So in Ralf's case four devices share IRQ 18,

two USB hubs, a soundcard and a graphics card. Each of those devices

gets its own specific softirq which then can get prioritized with rtirq

accordingly. Default rtprio is 50 afaik, so nvidia should get rtprio 50

and not 82.
> AFAIK it is not possible (or simple) to raise _just_ the soundcard as it

quoted text
> is impossible to know which irq process corresponds to a soundcard (and

> which one does not). That is because the labeling of the irq process

> names in the ps listing is arbitrary.

It is not arbitrary, the softirqs get specific names derived from the

loaded kernel module for that device iirc. So the graphics card gets a

label 18-nvidia, the soundcard 18-snd_hdsp and both usb hubs

18-ohci_usb. And it is those labels that rtirq uses to set the rtprio

for the different softirqs.
  At least that is what I remember

quoted text
> seeing last I looked at this issue. You can of course manually lower the

> priorities of non-soundcard irq processes with chrt.

>

> -- Fernando

More info:

http://wiki.linuxmusicians.com/doku.php?id=system_configuration#prioriti...
If that Wiki page contains errors, please let me know so I can correct

those.
Best,
Jeremy

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