2 May
2012
2 May
'12
9:19 a.m.
On 05/01/12 20:32, Fernando Lopez-Lezcano wrote:
(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
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
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#priorities
If that Wiki page contains errors, please let me know so I can correct
those.
Best,
Jeremy