From: Christian Borntraeger <borntraeger@de.ibm.com>
To: Davidlohr Bueso <dave@gnu.org>
Cc: Avi Kivity <avi@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>, KVM <kvm@vger.kernel.org>,
lkml <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] KVM: x86: add paging gcc optimization
Date: Thu, 08 Mar 2012 16:47:27 +0100 [thread overview]
Message-ID: <4F58D48F.8050807@de.ibm.com> (raw)
In-Reply-To: <1331207154.28711.2.camel@offworld>
On 08/03/12 12:45, Davidlohr Bueso wrote:
> From: Davidlohr Bueso <dave@gnu.org>
>
> Since most guests will have paging enabled for memory management, add likely() optimization
> around CR0.PG checks.
> {
> - return kvm_read_cr0_bits(vcpu, X86_CR0_PG);
> + return likely(kvm_read_cr0_bits(vcpu, X86_CR0_PG));
IMHO likely/unlikely should be considered more as fast-path/slow-path and not as often/less often.
Is that the case here? This patch might cause a mis-prediction for non-paging guests all
the time.
Non-paging might be really irrelevant, so I am just making a point, since
likely/unlikely is mis-used too often especially for "most users do it that way".
Christian
next prev parent reply other threads:[~2012-03-08 15:47 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-08 11:45 [PATCH v2] KVM: x86: add paging gcc optimization Davidlohr Bueso
2012-03-08 15:47 ` Christian Borntraeger [this message]
2012-03-08 21:27 ` Davidlohr Bueso
2012-03-12 12:12 ` Avi Kivity
2012-03-23 21:51 ` Davidlohr Bueso
2012-03-28 16:36 ` Avi Kivity
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