Re: [PATCH] KVM: Eliminate extra function calls in kvm_get_dirty_log_protect()

Marcelo Tosatti
2015-03-19T01:24:22Z

On Tue, Mar 17, 2015 at 09:58:21AM +0100, Paolo Bonzini wrote:
>
>
> On 17/03/2015 08:19, Takuya Yoshikawa wrote:
> > When all bits in mask are not set,
> > kvm_arch_mmu_enable_log_dirty_pt_masked() has nothing to do. But since
> > it needs to be called from the generic code, it cannot be inlined, and
> > a few function calls, two when PML is enabled, are wasted.
> >
> > Since it is common to see many pages remain clean, e.g. framebuffers can
> > stay calm for a long time, it is worth eliminating this overhead.
> >
> > Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
> > ---
> > virt/kvm/kvm_main.c | 8 +++++---
> > 1 file changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index a109370..420d8cf 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -1061,9 +1061,11 @@ int kvm_get_dirty_log_protect(struct kvm *kvm,
> > mask = xchg(&dirty_bitmap[i], 0);
> > dirty_bitmap_buffer[i] = mask;
> >
> > - offset = i * BITS_PER_LONG;
> > - kvm_arch_mmu_enable_log_dirty_pt_masked(kvm, memslot, offset,
> > - mask);
> > + if (mask) {
> > + offset = i * BITS_PER_LONG;
> > + kvm_arch_mmu_enable_log_dirty_pt_masked(kvm, memslot,
> > + offset, mask);
> > + }
> > }
> >
> > spin_unlock(&kvm->mmu_lock);
> >
>
> Good catch!
>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Applied, thanks.