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([2001:b07:6468:f312:9def:34a0:b68d:9993]) by smtp.gmail.com with ESMTPSA id h20sm23970095wrc.47.2020.03.05.06.35.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Mar 2020 06:35:46 -0800 (PST) Subject: Re: [PATCH] KVM: x86: small optimization for is_mtrr_mask calculation To: linmiaohe , rkrcmar@redhat.com, sean.j.christopherson@intel.com, vkuznets@redhat.com, jmattson@google.com, joro@8bytes.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org References: <1583376535-27255-1-git-send-email-linmiaohe@huawei.com> From: Paolo Bonzini Message-ID: <2b678644-fcc0-e853-a53c-2651c1f6a327@redhat.com> Date: Thu, 5 Mar 2020 15:35:45 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <1583376535-27255-1-git-send-email-linmiaohe@huawei.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/03/20 03:48, linmiaohe wrote: > From: Miaohe Lin > > We can get is_mtrr_mask by calculating (msr - 0x200) % 2 directly. > > Signed-off-by: Miaohe Lin > --- > arch/x86/kvm/mtrr.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c > index 7f0059aa30e1..a98701d9f2bf 100644 > --- a/arch/x86/kvm/mtrr.c > +++ b/arch/x86/kvm/mtrr.c > @@ -348,7 +348,7 @@ static void set_var_mtrr_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data) > int index, is_mtrr_mask; > > index = (msr - 0x200) / 2; > - is_mtrr_mask = msr - 0x200 - 2 * index; > + is_mtrr_mask = (msr - 0x200) % 2; > cur = &mtrr_state->var_ranges[index]; > > /* remove the entry if it's in the list. */ > @@ -424,7 +424,7 @@ int kvm_mtrr_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata) > int is_mtrr_mask; > > index = (msr - 0x200) / 2; > - is_mtrr_mask = msr - 0x200 - 2 * index; > + is_mtrr_mask = (msr - 0x200) % 2; > if (!is_mtrr_mask) > *pdata = vcpu->arch.mtrr_state.var_ranges[index].base; > else > If you're going to do that, might as well use ">> 1" for index instead of "/ 2", and "msr & 1" for is_mtrr_mask. Paolo