svn commit: r191405 - in head/sys: amd64/amd64 i386/i386

[John Baldwin]

On Wednesday 22 April 2009 6:03:04 pm Ceri Davies wrote:
> On Wed, Apr 22, 2009 at 05:59:04PM -0400, John Baldwin wrote:
> > On Wednesday 22 April 2009 5:40:37 pm John Baldwin wrote:
> > > Author: jhb
> > > Date: Wed Apr 22 21:40:37 2009
> > > New Revision: 191405
> > > URL: http://svn.freebsd.org/changeset/base/191405
> > > 
> > > Log:
> > >   Adjust the way we number CPUs on x86 so that we attempt to "group" all
> > >   logical CPUs in a package.  We do this by numbering the non-boot CPUs
> > >   by starting with the first CPU whose APIC ID is after the boot CPU and
> > >   wrapping back around to APIC ID 0 if needed rather than always starting
> > >   at APIC ID 0.  While here, adjust the cpu_mp_announce() routine to list
> > >   CPUs based on the mapping established by assign_cpu_ids() rather than
> > >   making assumptions about the algorithm assign_cpu_ids() uses.
> > 
> > An example is probably in order for this to make sense.  Suppose you have a 
> > system with two quad-core CPUs.  Package 0 has CPUs numbered 0, 1, 2, and 3.  
> > Package 1 has CPUs numbered 4, 5, 6, and 7.  With the old code, if package 0 
> > won the election to be the boot processor, then CPU 0 would be the BSP and 
> > the logical IDs would match the APIC IDs.  However, if package 1 won the 
> > election during POST, then CPU 0 would be APIC ID 4 on package 0 followed by 
> > CPU 1 being APIC ID 0, CPU 2 being APIC ID 1, etc.  Thus, when CPU 0 was the 
> > boot CPU you had a nice grouping where CPUs 0-3 were a single package and 
> > CPUs 4-7 were another package.  However, when CPU 4 was the boot CPU, CPUs 0 
> > and 5-7 where one package, and CPUs 1-4 where the second package.  The effect 
> > of this patch is to change the case when CPU 4 is the boot CPU such that CPUs 
> > 0-3 are now all from CPU 4's package (APIC IDs 4-7), and CPUs 4-7 are from 
> > the other package (APIC IDs 0-3).  What this means, in turn, is that in both 
> > cases you now always have CPUs 0-3 as one package and CPUs 4-7 as another 
> > package regardless of which CPU wins the boot-time election.
> 
> What if I have HT turned on?  Do they bunch up with the "real" CPU IDs
> or all together at the end?

They will be bunched up as they were previously when CPU 0 was the BSP.  For
Intel at least (and I think AMD is the same), a given package consumes one
contiguous range of physical APIC IDs.

-- 
John Baldwin