Date: Fri, 16 Mar 2001 07:52:34 -0800 (PST) From: Matthew Jacob <mjacob@feral.com> To: Alfred Perlstein <bright@wintelcom.net> Cc: Benno Rice <benno@FreeBSD.ORG>, Doug Rabson <dfr@nlsystems.com>, John Baldwin <jhb@FreeBSD.ORG>, arch@FreeBSD.ORG Subject: page faults in AIX kernel Message-ID: <Pine.BSF.4.21.0103160744260.53255-100000@beppo.feral.com> In-Reply-To: <20010316073921.W29888@fw.wintelcom.net>
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On Fri, 16 Mar 2001, Alfred Perlstein wrote:
> * Matthew Jacob <mjacob@feral.com> [010316 07:28] wrote:
> >
> > > >
> > > > (in the PPC architecture I believe that page faults are interrupts)
> > >
> > > Not quite. Page faults and external interrupts are both classed as
> > > 'exceptions'. External interrupts however can be turned on or off using the
> > > EE bit of the machine state register without disabling page fault (DSI or ISI)
> > > exceptions.
> >
> > Ah! Thanks for the clarification.
> >
> > What I had gotten my notion from was from AIX- if you have a spinlock
> > contested and take a page fault in the kernel, you lock up.
>
> I've heard that page faults in the AIX kernel are "ok" (obviously
> not when holding a mutex) because some of the kernel memory is
> actually pageable.
>
> Any idea on what structures they keep in pageable memory?
>
> (just wondering)
They have a concept of pinned and unpinned memory. IIRC (it's been a while
now- one of my former clients took back the 2 processor 300MHz PPC box about
a year ago and I hadn't done any work with it for 2-3 years) pinned memory
isn't unpageable while unpinned memory is.... Let's see if I can dig up some
examples... I can't remember exactly what other 'structures' they then
actually have as pageable... I guess pretty much anything that isn't pinned
(now isn't *that* a useful answer) :-)..
Okay- here's one:
/*
* If this is the first time through:
* Add entry to the device switch table to call this driver
*/
if (nconfigured == 0) {
result = devswadd(dev, &vtd_dsw);
if (result != 0) {
Trace1(0, "vtd_config: devswadd result: %d", result);
break;
}
result = pincode((int (*) ()) vtd_timer);
if (result) {
Trace1(0, "vtd_config: pincode result: %d", result);
devswdel(dev);
break;
}
}
nconfigured++;
Note that the timer funcion is pinned so that it can't be paged out when a
soft call happens (which would be embarrassing).
-matt
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