[illumos-Developer] Available MSI(-x) interrupt limit.

[Dmitry Yusupov]

Who came up with 2? Why not 3 or 8? Why not 1 ? :-)

This is obviously wrong way to limit system and lock user into pre-MSI
days... But do I understand you correctly that driver can allocate more
than 2 if needed? Can you please post an example of snippet code in
here?

> -----Original Message-----
> From: Garrett D'Amore
> Sent: Tuesday, June 07, 2011 10:53 AM
> To: Dmitry Yusupov
> Cc: Alexey Zaytsev; illumos-dev
> Subject: Re: [illumos-Developer] Available MSI(-x) interrupt limit.
> 
> You misunderstand.  The default is 2 now.  If you want more, it take
> extraordinary measures.
> 
> On illumos there is a more modern API that allows "cooperative" device
> drivers to get more, with a promise that they will yield the resources
if other
> devices need them later.
> 
>   -- Garrett D'Amore
> 
> On Jun 7, 2011, at 8:59 PM, "Dmitry Yusupov" <dmitry at nexenta.com>
> wrote:
> 
> > This seems like not logical way to fix ill driver... :-) Instead of
> > harming overall system performance we should fix the driver(s). And
> > those vendors who ships Illumos can apply limiting settings if they
> > care. I would guess that in most cases they will not use Illumos
with
> > devices/drivers which would consume all the interrupts and would
> > rather prefer to focus the driver...
> >
> > Why don't we reverse this default setting from max to min ?
> >
> >> -----Original Message-----
> >> From: Garrett D'Amore [mailto:garrett at nexenta.com]
> >> Sent: Tuesday, June 07, 2011 7:51 AM
> >> To: Alexey Zaytsev
> >> Cc: illumos-dev
> >> Subject: Re: [illumos-Developer] Available MSI(-x) interrupt limit.
> >>
> >> Yes.    The limit comes from the fact that ill behaved
devices/drivers
> > could
> >> easily consume all the interrupts on a system, preventing other
> > devices from
> >> attaching.  There was a recent rearchitecture of the interrupt code
> >> specifically for MSI-X that offers far more interrupt vectors to
> > devices, in
> >> exchange for the device registering a callback indicating a
> > willingness to
> >> return interrupts back to the system when they become scarce.
> >>
> >> There's also a legacy override somewhere that you can use for
> >> specific devices, but it isn't documented.  I don't remember the
name
> >> of the
> > override,
> >> but it can grow the set up to 8.
> >>
> >>  -- Garrett D'Amore
> >>
> >> On Jun 7, 2011, at 5:49 PM, "Alexey Zaytsev"
> > <alexey.zaytsev at gmail.com>
> >> wrote:
> >>
> >>> Hey.
> >>>
> >>> Any ideas, what's the reason to have the 2 msi per device limit?
> >>> It's been there from the start of the history.
> >>>
> >>> https://github.com/illumos/illumos-
> >> gate/blob/master/usr/src/uts/common/os/ddi_intr_impl.c#L296
> >>> https://github.com/illumos/illumos-
> >> gate/blob/master/usr/src/uts/common/os/ddi_intr_impl.c#L40
> >>> https://github.com/illumos/illumos-
> >> gate/blob/master/usr/src/uts/common/sys/ddi_intr_impl.h#L146
> >>>
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