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SubjectRe: lmbench lat_mmap slowdown with CONFIG_PARAVIRT
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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



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