From mboxrd@z Thu Jan  1 00:00:00 1970
From: Takuya Yoshikawa <takuya.yoshikawa@gmail.com>
Subject: Re: [RFC PATCH 3/3] KVM: MMU: Optimize guest page table walk
Date: Fri, 29 Apr 2011 15:30:58 +0900
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Cc: Andi Kleen <andi@firstfloor.org>, Avi Kivity <avi@redhat.com>,
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To: Takuya Yoshikawa <takuya.yoshikawa@gmail.com>
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On Fri, 29 Apr 2011 14:38:08 +0900
Takuya Yoshikawa <takuya.yoshikawa@gmail.com> wrote:

> On Thu, 28 Apr 2011 19:46:00 -0700
> Andi Kleen <andi@firstfloor.org> wrote:
> 
> > Avi Kivity <avi@redhat.com> writes:
> > >
> > > Good optimization.  copy_from_user() really isn't optimized for short
> > > buffers, I expect much of the improvement comes from that.
> > 
> > Actually it is equivalent to get_user for the lenghts supported by
> > get_user, assuming you pass in a constant length. You probably do not.
> > 
> > -Andi
> 
> 
> Weird, I actually measured some changes even after dropping other parts
> than get_user() usage.
> 
> Only I can guess for that reason is the reduction of some function calls
> by inlining some functions.

A bit to clarify.

Original path:

  kvm_read_guest_page_mmu()
    kvm_read_guest_page()
      copy_from_user()

Takuya