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From:   Wanpeng Li <kernellwp@gmail.com>
Date:   Fri, 6 Mar 2020 10:27:26 +0800
Message-ID: <CANRm+CwRPDpvN_gcO=VbuukjEL2=OPYnxtqoJO6vTk4Z3nudvQ@mail.gmail.com>
Subject: Re: [PATCH] KVM: x86: small optimization for is_mtrr_mask calculation
To:     linmiaohe <linmiaohe@huawei.com>
Cc:     "hpa@zytor.com" <hpa@zytor.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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        "rkrcmar@redhat.com" <rkrcmar@redhat.com>,
        "sean.j.christopherson@intel.com" <sean.j.christopherson@intel.com>,
        "vkuznets@redhat.com" <vkuznets@redhat.com>,
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        "joro@8bytes.org" <joro@8bytes.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
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On Fri, 6 Mar 2020 at 10:23, linmiaohe <linmiaohe@huawei.com> wrote:
>
> hpa@zytor.com wrote:
> >>On March 5, 2020 6:05:40 PM PST, linmiaohe <linmiaohe@huawei.com> wrote:
> >>Hi,
> >>Paolo Bonzini <pbonzini@redhat.com> wrote:
> >>Many thanks for suggestion. What do you mean is like this ?
> >>
> >>      index = (msr - 0x200) >> 1;
> >>      is_mtrr_mask = msr & 1;
> >>
> >>Thanks again.
> >
> >You realize that the compiler will probably produce exactly the same code, right? As such, it is about making the code easy for the human reader.
> >
> >Even if it didn't, this code is as far from performance critical as one can possibly get.
>
> Yep, it looks gain little. Thanks.

Please post the performance number when you mention optimize XXX later.

    Wanpeng