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SubjectRe: lmbench lat_mmap slowdown with CONFIG_PARAVIRT
On Tue, Jan 20, 2009 at 09:56:53PM +0100, Ingo Molnar wrote:
>
> * Jeremy Fitzhardinge <jeremy@goop.org> wrote:
> >> | 50234816 | 51303520 cache references +2.12%
> >> | 5428258 | 5583728 cache misses +2.86%
> >>
> >
> > Is this I or D, or combined?
>
> That's last-level-cache references+misses (L2 cache):
>
> Bit Position Event Name UMask Event Select
> CPUID.AH.EBX
> 3 LLC Reference 4FH 2EH
> 4 LLC Misses 41H 2EH

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?

It would be interesting to see how "the oltp" benchmark fares with
CONFIG_PARAVIRT turned on. That workload lives and dies by the cache :)


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