[LAU] rtirq, kernels >= 3.2 and udev

Fernando Lopez-Lezcano nando at ccrma.Stanford.EDU
Wed May 9 18:23:42 UTC 2012

On 05/09/2012 07:38 AM, Rui Nuno Capela wrote:
> On 05/09/2012 02:03 AM, Fernando Lopez-Lezcano wrote:
>> PS: Another rtirq script in /etc/pm/sleep.d/ could save the current
>> priorities before a suspend and restore them after a resume - that does
>> not happen currently.
> what about just `rtirq restart` on the sleep.d script (on thaw|resume) ?
> warning. there's no state salvage being done on bad old rtirq script. in
> fact `rtirq stop` is a plain nop by default, unless RTIRQ_RESET_ALL=1 is
> set (cf. /etc/rtirq.conf aka. /etc/sysconfig/rtirq) which makes all
> target irq service threads to reset to rtprio=50 but also to "normal"
> scheduling class(SCHED_OTHER). might not on par with the times :)

Yes, probably not on par with the times as when using threaded irqs they 
run by default SCHED_FIFO and with priority = 50 (I don't know if the 
priority is fixed or can be changed by, say, a kernel boot parameter).

> note that `rtirq restart` is actually the same function as `rtirq stop`
> immediately followed by `rtirq start`. however, as s the very same irq
> service threads are at stake, this whole remark might not be an issue
> after all:)

I like the idea of using udev for setting priorities of soundcard 
interrupts as that allows you to run with the least amount of high 
priority processes (only for the cards actually present). In particular 
for usb cards only the usb irq that corresponds to the card needs to be 
raised and then it returns to normal when the card is unplugged.

-- Fernando

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