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

[John Baldwin]

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.

-- 
John Baldwin