Re: [PATCH] x86: add /proc/cpuinfo/physical id quirks

[Alex Chiang <achiang@hp.com>]

* Suresh Siddha <suresh.b.siddha@intel.com>:
> On Fri, 2009-08-14 at 09:36 -0700, Alex Chiang wrote:
> > As systems become larger and more complex, it is not always possible
> > to assume that an APIC ID maps directly to a given physical slot.
> > 
> > From a UI point-of-view, it's nice if the 'physical id' field in
> > /proc/cpuinfo matches the silk-screening or labelling on the system
> > chassis.
> > 
> > Add a quirk that allows oddball platforms to ensure that what the kernel
> > displays in /proc/cpuinfo matches the physical reality.
> 
> Alex, Does it makes sense to add a new entry in /proc/cpuinfo rather
> than overloading the 'physical id' by modifying phys_proc_id.

Hm, I'm not entirely sure about that, for two reasons.

First (and this is the weaker reason), I'd prefer not to keep
adding new fields to /proc/cpuinfo if we can help it, as it just
makes for a continually more complicated ABI/API for userspace.

Second, I guess I'm not sure what else 'physical id' /should/
represent. I'm willing to be corrected on this point, so if I'm
wrong, just call it simple ignorance. :)

> That way, even if there is a mis-match between the bios and the
> OS fixup tables, we won't screw up other topology setup etc in
> the kernel that are dependent on the phys_proc_id.

My quick grep earlier led me to believe that as long as the
phys_proc_ids were /consistent/ then it didn't seem to matter
what their /values/ were.

In other words, my patch simply says, "all cores that had
phys_proc_id X now have phys_proc_id Y". All the cores on a
physical package have identical phys_proc_ids, and cores on a
different physical package do /not/ collide.

But again, that just might be my ignorance again. If we do indeed
care about the values of phys_proc_ids, please let me know and
I'd be happy to rework the patch.

Thanks.

/ac