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

Takuya Yoshikawa
2015-03-17T07:19:58Z

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