From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932252AbbCQI6d (ORCPT ); Tue, 17 Mar 2015 04:58:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56966 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754339AbbCQI60 (ORCPT ); Tue, 17 Mar 2015 04:58:26 -0400 Message-ID: <5507ECAD.1030908@redhat.com> Date: Tue, 17 Mar 2015 09:58:21 +0100 From: Paolo Bonzini User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 MIME-Version: 1.0 To: Takuya Yoshikawa CC: kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] KVM: Eliminate extra function calls in kvm_get_dirty_log_protect() References: <20150317161958.991bd7dc36c714f6498821db@lab.ntt.co.jp> In-Reply-To: <20150317161958.991bd7dc36c714f6498821db@lab.ntt.co.jp> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@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