From: David Laight <David.Laight@ACULAB.COM>
To: 'Paolo Bonzini' <pbonzini@redhat.com>,
linmiaohe <linmiaohe@huawei.com>,
"rkrcmar@redhat.com" <rkrcmar@redhat.com>,
"sean.j.christopherson@intel.com"
<sean.j.christopherson@intel.com>,
"vkuznets@redhat.com" <vkuznets@redhat.com>,
"jmattson@google.com" <jmattson@google.com>,
"joro@8bytes.org" <joro@8bytes.org>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"mingo@redhat.com" <mingo@redhat.com>,
"bp@alien8.de" <bp@alien8.de>, "hpa@zytor.com" <hpa@zytor.com>
Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>
Subject: RE: [PATCH] KVM: x86: small optimization for is_mtrr_mask calculation
Date: Thu, 5 Mar 2020 15:10:06 +0000 [thread overview]
Message-ID: <dc1870b0ea164015b1c1b6bc4d3248fe@AcuMS.aculab.com> (raw)
In-Reply-To: <2b678644-fcc0-e853-a53c-2651c1f6a327@redhat.com>
From: Paolo Bonzini
> Sent: 05 March 2020 14:36
>
> On 05/03/20 03:48, linmiaohe wrote:
> > From: Miaohe Lin <linmiaohe@huawei.com>
> >
> > We can get is_mtrr_mask by calculating (msr - 0x200) % 2 directly.
> >
> > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> > ---
> > 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.
Provided the variables are unsigned it makes little difference
whether you use / % or >> &.
At least with / % the two values are the same.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2020-03-05 15:10 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-05 2:48 [PATCH] KVM: x86: small optimization for is_mtrr_mask calculation linmiaohe
2020-03-05 14:35 ` Paolo Bonzini
2020-03-05 15:10 ` David Laight [this message]
2020-03-05 15:25 ` Paolo Bonzini
2020-03-06 2:05 linmiaohe
2020-03-06 2:09 ` hpa
2020-03-06 2:22 linmiaohe
2020-03-06 2:27 ` Wanpeng Li
2020-03-06 2:30 linmiaohe
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=dc1870b0ea164015b1c1b6bc4d3248fe@AcuMS.aculab.com \
--to=david.laight@aculab.com \
--cc=bp@alien8.de \
--cc=hpa@zytor.com \
--cc=jmattson@google.com \
--cc=joro@8bytes.org \
--cc=kvm@vger.kernel.org \
--cc=linmiaohe@huawei.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=pbonzini@redhat.com \
--cc=rkrcmar@redhat.com \
--cc=sean.j.christopherson@intel.com \
--cc=tglx@linutronix.de \
--cc=vkuznets@redhat.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).