7.1-STABLE does not boot after recent superpage support MFC

[John Baldwin]

On Friday 27 February 2009 11:21:00 am Michael Butler wrote:
> John Baldwin wrote:
> > On Friday 27 February 2009 8:08:30 am Igor Sysoev wrote:
> >
> >> And the message is cycled. The kernel does not boot despite
> >> vm.pmap.pg_ps_enabled value.
> >
> > This should now be fixed, apologies for the breakage. :(
> 
> What are the benefits and/or impacts of enabling this?
> 
> Is there anything to be gained with respect to cache and/or TLB
> utilization in allowing entry promotion through a reduced "footprint" or
> similar? How much does this depend on architecture, say, e.g. Core-2 Duo
> vs. Pentium?

Yes there are gains due to what you mention, but it does depend on the 
specific processor and specifically the how it manages entries for large 
pages in its TLB (some processsors have separate TLB entries for large pages 
and have very few of them, others can store either a small or lage page in a 
single TLB slot, etc.).  Alan knows far more of the details of this than I 
do.

> I note that it is not enabled by default in -current either - just curious,

Actually, it is enabled by default on amd64 in current.

-- 
John Baldwin