Re: lmbench lat_mmap slowdown with CONFIG_PARAVIRT

[Zachary Amsden <zach@vmware.com>]

On Wed, 2009-01-21 at 14:23 -0800, Jeremy Fitzhardinge wrote:
> Nick Piggin wrote:
> > Oh, _llc_ references/misses? Ouch.
> >
> > You have, what 32K L1I, 32K L1D, and 4MB L2? And even this microbenchmark
> > is seeing increased L2 misses by nearly 3%. Hmm, I wonder where that is
> > coming from? Instruction fetches?
> >   
> 
> I assume so.  There should be no extra data accesses with 
> CONFIG_PARAVIRT (hm, there's probably some extra stack/spill traffic, 
> but I surely hope that's not falling out of cache).

These fragments, from native_pgd_val, certainly don't help:

c0120f60:       55                      push   %ebp
c0120f61:       89 e5                   mov    %esp,%ebp
c0120f63:       5d                      pop    %ebp
c0120f64:       c3                      ret
c0120f65:       8d 74 26 00             lea    0x0(%esi,%eiz,1),%esi
c0120f69:       8d bc 27 00 00 00 00    lea    0x0(%edi,%eiz,1),%edi

That is really disgusting.  We absolutely should be patching away the
function calls here in the native case.. not sure we do that today.

Zach