From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH] KVM: Eliminate extra function calls in kvm_get_dirty_log_protect() Date: Tue, 17 Mar 2015 09:58:21 +0100 Message-ID: <5507ECAD.1030908@redhat.com> References: <20150317161958.991bd7dc36c714f6498821db@lab.ntt.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: Takuya Yoshikawa Return-path: In-Reply-To: <20150317161958.991bd7dc36c714f6498821db@lab.ntt.co.jp> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 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 > --- > 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