* [PATCH] KVM: Eliminate extra function calls in kvm_get_dirty_log_protect()
@ 2015-03-17 7:19 Takuya Yoshikawa
2015-03-17 8:58 ` Paolo Bonzini
0 siblings, 1 reply; 3+ messages in thread
From: Takuya Yoshikawa @ 2015-03-17 7:19 UTC (permalink / raw)
To: pbonzini; +Cc: kvm, linux-kernel
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);
--
2.1.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] KVM: Eliminate extra function calls in kvm_get_dirty_log_protect()
2015-03-17 7:19 [PATCH] KVM: Eliminate extra function calls in kvm_get_dirty_log_protect() Takuya Yoshikawa
@ 2015-03-17 8:58 ` Paolo Bonzini
2015-03-19 1:23 ` Marcelo Tosatti
0 siblings, 1 reply; 3+ messages in thread
From: Paolo Bonzini @ 2015-03-17 8:58 UTC (permalink / raw)
To: Takuya Yoshikawa; +Cc: kvm, linux-kernel
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>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] KVM: Eliminate extra function calls in kvm_get_dirty_log_protect()
2015-03-17 8:58 ` Paolo Bonzini
@ 2015-03-19 1:23 ` Marcelo Tosatti
0 siblings, 0 replies; 3+ messages in thread
From: Marcelo Tosatti @ 2015-03-19 1:23 UTC (permalink / raw)
To: Paolo Bonzini; +Cc: Takuya Yoshikawa, kvm, linux-kernel
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.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2015-03-19 1:24 UTC | newest]
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2015-03-17 7:19 [PATCH] KVM: Eliminate extra function calls in kvm_get_dirty_log_protect() Takuya Yoshikawa
2015-03-17 8:58 ` Paolo Bonzini
2015-03-19 1:23 ` Marcelo Tosatti
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