On 29 Jan 2009, at 17:51, Andriy Gapon wrote:
on 29/01/2009 19:17 Rui Paulo said the following:
On 29 Jan 2009, at 11:47, Andriy Gapon wrote:
INTR_FILTER - what does it do?
It doesn't seem to be documented anywhere, but seems to affect
interrupt
code.
INTR_FILTER allows you to skip the FILTER+ITHREAD headache.
Could you please explain a little bit what is this headache?
Basically, you use filter + ithread (intr_filter) when you want to do
more than basic things in your interrupt handler routine. For example,
allocating memory must be done in a ithread, it can't be done on the
interrupt routine.
I thought, similarly to what Ed said, that in filter one could quickly
check for a stray interrupt (or shared interrupt from other device)
and
in ithread one could perform meaningful work.
That's right. But INTR_FILTER does all the filter + ithread setup for
you via FILTER_SCHEDULE_THREAD.
But I also had some doubts about what is legal and what is illegal in
ithread. E.g. could I take a non-spin mutex or wait on a condvar? I
guess not - because in the case of shared interrupts the same
ithread is
used to handle everything.
See dev/asmc/asmc.c for an example.
Thank you, the example is enlightening. But also one has to look into
how "the framework" works (or just know it) to understand why things
are
done this way but not the other. E.g. why you have to use a
taskqueue in
non-INTR_FILTER case.
I needed a taskqueue because devctl_notify() calls malloc and you
can't call malloc (which holds some type of lock, I can't remember)
from an interrupt context (asmc_sms_intrfast())
BTW, INTR_FILTER seems quite useful. Why, then, it is not the default?
The drivers would have to be ported to INTR_FILTER. Right now, only
asmc is using INTR_FILTER, so I don't think there is much gain in
making it the default.
--
Rui Paulo
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