Re: Priorities of IRQ handlers

[Arnaldo Carvalho de Melo <acme@ghostprotocols.net>]

Em Wed, Nov 28, 2007 at 08:12:24AM -0600, K.R. Foley escreveu:
> John Sigler wrote:
> > Hello Steven,
> > 
> > Steven Rostedt wrote:
> > 
> >> John Sigler wrote:
> >>
> >>> I need to change the priorities of several soft and hard IRQ handlers.
> >>>
> >>> Namely,
> >>>
> >>> o reduce the prio of "softirq-timer" handler to 10
> >>>
> >>> o reduce the prio of IRQ14 and IRQ15 handlers to 20
> >>>    (my flash drives do not support DMA BTW...)
> >>>
> >>> o boost the prio of my I/O boards' IRQ handlers to 60
> >>>    (there can be 1 or 2 boards, the driver is a kernel module
> >>>     which is loaded after the system has booted.)
> >>>
> >>> I've written a short program that calls
> >>>    sched_setscheduler(pid, SCHED_FIFO, &param);
> >>> with the appropriate pid, which I look up using ps -ef
> >>
> >> Look for the program "chrt". It does this for you. This program is
> >> available in all major distributions of Linux.
> > 
> > Thanks for the tip.
> > 
> > For the record, I found schedutils on Robert Love's page:
> > 
> > http://rlove.org/
> > http://rlove.org/misc/schedutils-1.5.0.tar.gz
> > 
> > However, I had already solved that part of the problem with a
> > program of my own.
> > 
> > My real problem is: the IRQ handlers for the I/O boards are
> > only instantiated when the kernel module is inserted. How do
> > I /reliably/ determine their pid?
> 
> What about something like:
> chrt -f -p 99 `/sbin/pidof 'IRQ 8'`

If he knows that IRQ 8 is associated with his device, that is ok,
but how to map device -> IRQ in the first place?
 
> > 
> > e.g. on one system, the IRQ handler for my I/O board is IRQ5
> > with pid 745. On another system, it's IRQ20 with pid 808.
> > On a third system they're IRQ20 and IRQ21 with pid 239 and 240.

See?

Perhaps he could use a kernel command line where he would tell that
for the string used in request_irq the kthread priority should be N.

IIRC there was somebody trying to write a patch to support this at some
point in this list...

- Arnaldo