linux-kernel - Re: [PATCH v2 06/12] KVM: MMU: introduce a static table to map guest access to spte access

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Message-ID: <5101F207.6040603@linux.vnet.ibm.com>
Date:	Fri, 25 Jan 2013 10:46:31 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Avi Kivity <avi.kivity@...il.com>, Gleb Natapov <gleb@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 06/12] KVM: MMU: introduce a static table to map guest
 access to spte access

On 01/25/2013 08:15 AM, Marcelo Tosatti wrote:
> On Wed, Jan 23, 2013 at 06:07:20PM +0800, Xiao Guangrong wrote:
>> It makes set_spte more clean and reduces branch prediction
>>
>> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
>> ---
>>  arch/x86/kvm/mmu.c |   37 ++++++++++++++++++++++++++-----------
>>  1 files changed, 26 insertions(+), 11 deletions(-)
> 
> Don't see set_spte as being a performance problem?
> IMO the current code is quite simple.

Yes, this is not a performance problem.

I just dislike this many continuous "if"-s in the function:

if (xxx)
	xxx
if (xxx)
	xxx
....

Totally, it has 7 "if"-s before this patch.

Okay, if you think this is unnecessary, i will drop this patch. :)

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