linux-kernel - Re: [PATCH] KVM: x86: small optimization for is_mtrr

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Message-ID: <4e9d847ea5d54e4fa83f3bb910242e16@huawei.com>
Date:   Fri, 6 Mar 2020 02:22:57 +0000
From:   linmiaohe <linmiaohe@...wei.com>
To:     "hpa@...or.com" <hpa@...or.com>
CC:     Paolo Bonzini <pbonzini@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "sean.j.christopherson@...el.com" <sean.j.christopherson@...el.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "jmattson@...gle.com" <jmattson@...gle.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>
Subject: Re: [PATCH] KVM: x86: small optimization for is_mtrr_mask calculation

hpa@...or.com wrote:
>>On March 5, 2020 6:05:40 PM PST, linmiaohe <linmiaohe@...wei.com> wrote:
>>Hi,
>>Paolo Bonzini <pbonzini@...hat.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.