SMP detection

[backyard]

--- Jordi Carrillo <jordilin at gmail.com> wrote:

> 2006/8/31, Skylar Thompson <skylar at cs.earlham.edu>:
> >
> > Michal Mertl wrote:
> > > No! Kernel threads (e.g. handling interrupts)
> aren't that much different
> > > to normal processes.
> > >
> > > Logical CPUs on a single HTT capable CPU share
> most of the CPU logic,
> > > especially all the external stuff (handling
> interrupts). Scheduling
> > > handling of interrupts on the
> "secondary/logical" core  wouldn't
> > > probably help performance at all (if that is at
> all possible).
> > >
> >
> > Could you clarify note 20031022 in
> /usr/src/UPDATING? It states that HTT
> > CPUs are used for interrupts if they are detected,
> even if they aren't
> > used by regular processes. Was this something that
> just showed up in
> > pre-6.x releases?
> >
> > --
> > -- Skylar Thompson (skylar at cs.earlham.edu)
> > -- http://www.cs.earlham.edu/~skylar/
> >
> >
> >
> >
> > Another question that's wondering me is why
> FreeBSD with the SMP kernel
> the gnome system monitor (Applications->System
> Tools->System Monitor) only
> shows one CPU when Linux with a SMP kernel shows two
> CPUs
> 
> 
> -- 
> http://jordilin.wordpress.com
> 

I'm assuming you talking about an HT SMP scenario...
Linux is running the second core, but *BSD will not
unless you tell it too. I'll check with my dually once
I get home but I'm fairly certain even if your running
an SMP kernel if the other CPU isn't used, it isn't
going to tell you what processes are running on it,
because nothing is scheduled to run on it. Linux
doesn't care about the possible exploits and so by
default runs both HT cores.

Look at it like this I have two hands, I could put two
P99C-ASs in them, but if only one has a magazine in it
why and I going to claim I got two pieces??? Basically
by not setting the "...hyperthreading_allowed..."
variable you have removed the magazine from one of
your cores...

But I will check because I seem to recall there being
some kind of issue like this with my 5.4 box that I
just kind of shrugged off at the time. I thought it
was with KDE not gnome though... It should show both
or all your cores and what is running. But it can't
show you what is running on a CPU the kernel has
disavowed.

-brian