linux-kernel - Re: [PATCH 5/6] KVM: Separate rmap_pde from kvm_lpage_info->write

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Message-ID: <4FF105D0.8010400@linux.vnet.ibm.com>
Date:	Mon, 02 Jul 2012 10:22:08 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>,
	mtosatti@...hat.com, agraf@...e.de, paulus@...ba.org,
	aarcange@...hat.com, kvm@...r.kernel.org, kvm-ppc@...r.kernel.org,
	linux-kernel@...r.kernel.org, takuya.yoshikawa@...il.com
Subject: Re: [PATCH 5/6] KVM: Separate rmap_pde from kvm_lpage_info->write_count

On 06/29/2012 01:39 AM, Avi Kivity wrote:

> But I still think it's the right thing since it simplifies the code.
> Maybe we should add a prefetch() on write_count do mitigate the
> overhead, if it starts showing up in profiles.
> 

Long time ago, there was a discussion about dropping prefetch in the
operation of list walking:
	http://lwn.net/Articles/444336/
IIRC, the conclusion is that it is better to let CPU prefetch memory
by itself.

Actually, when i developed lockless spte walking, i measure the performance if
prefetch was used, but i did not see the improvement.


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