Re: Interrupt routine usage not shown by top in 8.0

--- On Tue, 3/17/09, Robert Watson <rwatson_at_FreeBSD.org> wrote:

> From: Robert Watson <rwatson_at_FreeBSD.org>
> Subject: Re: Interrupt routine usage not shown by top in 8.0
> To: "Paolo Pisati" <p.pisati_at_oltrelinux.com>
> Cc: "Barney Cordoba" <barney_cordoba_at_yahoo.com>, current_at_freebsd.org
> Date: Tuesday, March 17, 2009, 11:24 AM
> On Tue, 17 Mar 2009, Paolo Pisati wrote:
> 
> > perhaps i misunderstood your question, but i'll
> try to explain a bit:
> > 
> > before 7.0, bus_setup_intr() took just one function
> thus you could have an INTR_FAST or an INTR_MPSAFE handler,
> and you choose the kind of handler via a flag (INTR_FAST in
> this case).
> > 
> > after 7.0, bus_setup_intr() took 2 functions, thus you
> could have: a fast handler (aka filter), or an ithread
> handler (aka mpsafe), or a fast + ithread handler (available
> only with INTR_FILTER turned on).
> > 
> > in bus_setup_intr() the first function pointer is for
> the filter side of the handler, while the second pointer is
> for the ithread part, and if you declare both you can filter
> events (interrupts) and call the rest of the device driver
> (the ithread part) after the filter has recognized and
> acknowledged&masked the interrupt.
> 
> This clarifies my misunderstanding, thanks!
> 

I'd still be interested in knowing the specific advantage/consequences
of a fast filter vs an MPSAFE ithread?

In what circumstance would using a filter and then launching a task be 
advantageous over just using an ithread?

Barney