Re: [patch] Real-Time Preemption, -VP-2.6.9-rc4-mm1-U0

[Ingo Molnar]

* Florian Schmidt <mista.tapas@xxxxxxx> wrote:

> Cool :)
> 
> Say, does it still apply that one should not use unthreaded IRQ
> handlers for all IRQ's when using PREEMPT_REALTIME (Except maybe for
> the keyboard)?

yes - and this kernel simply does not allow the un-threading of
interrupt handlers anymore, so you cannot accidentally misconfigure it. 
(Not even the keyboard interrupt is an exception, it would have
lock-ripple-effects elsewhere.)

so the preferred (and only) interface to mark interrupts 'high prio' is
via process priorities. Starting from the -U1 kernel it will be possible
to do this:

   chrt -f 60 -p `ps -C 'IRQ:1' -o pid=`
   chrt -f 60 -p `ps -C 'IRQ:8' -o pid=`

this sets the keyboard and the RT-timer interrupt to FIFO:60.

In -U0 this is not possible because 'ps -C' does not handle kernel
threads with a space in their name. So there you'd need some wacky thing
like:

   chrt -f 60 -p `ps ax -o pid= -o comm= | grep "IRQ 1$" | cut -dI -f1`
   chrt -f 60 -p `ps ax -o pid= -o comm= | grep "IRQ 8$" | cut -dI -f1`

(someone should fix procps - or does it intentionally break with
whitespace command-strings?)

	Ingo
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