From a3c870bdce4d34332ebdba7eb9969592c4c6b243 Mon Sep 17 00:00:00 2001 From: Luca Tettamanti Date: Tue, 19 Jun 2007 22:41:38 +0200 Subject: [PATCH] KVM: Avoid useless memory write when possible When writing to normal memory and the memory area is unchanged the write can be safely skipped, avoiding the costly kvm_mmu_pte_write. Signed-Off-By: Luca Tettamanti Signed-off-by: Avi Kivity --- drivers/kvm/kvm_main.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c index 7826f16271e5..5603000573ec 100644 --- a/drivers/kvm/kvm_main.c +++ b/drivers/kvm/kvm_main.c @@ -1170,8 +1170,10 @@ static int emulator_write_phys(struct kvm_vcpu *vcpu, gpa_t gpa, return 0; mark_page_dirty(vcpu->kvm, gpa >> PAGE_SHIFT); virt = kmap_atomic(page, KM_USER0); - kvm_mmu_pte_write(vcpu, gpa, virt + offset, val, bytes); - memcpy(virt + offset_in_page(gpa), val, bytes); + if (memcmp(virt + offset_in_page(gpa), val, bytes)) { + kvm_mmu_pte_write(vcpu, gpa, virt + offset, val, bytes); + memcpy(virt + offset_in_page(gpa), val, bytes); + } kunmap_atomic(virt, KM_USER0); return 1; } -- 2.20.1