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SubjectRe: [benchmark] 1% performance overhead of paravirt_ops on native kernels


On Tue, 9 Jun 2009, Ingo Molnar wrote:
>
> In practice the pte format hurts the VM more than just highmem. (the
> two are inseparably connected of course)

I think PAE is a separate issue (ie I think HIGHMEM4G and HIGHMEM64G are
about different issues).

I do think we could probably drop PAE some day - very few 32-bit x86's
have more than 4GB of memory, and the ones that did buy lots of memory
back when it was a big deal for them have hopefully upgraded long since.

Of course, PAE also adds the NX flag etc, so there are probably other
reasons to have it. And qutie frankly, PAE is just a small x86-specific
detail that doesn't hurt anybody else.

So I have no reason to really dislike PAE per se - the real dislike is for
HIGHMEM itself, and that gets enabled already for HIGHMEM4G without any
PAE.

Of course, I'd also not ever enable it on any machine I have. PAE does add
overhead, and the NX bit isn't _that_ important to me.

Linus


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