linux-kernel - Re: [RFC PATCH v1 3/5] KVM: Add paravirt kvm_flush_tlb

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Message-ID: <1335885103.13683.147.camel@twins>
Date:	Tue, 01 May 2012 17:11:43 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>, mingo@...e.hu,
	jeremy@...p.org, mtosatti@...hat.com, kvm@...r.kernel.org,
	x86@...nel.org, vatsa@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org, hpa@...or.com
Subject: Re: [RFC PATCH v1 3/5] KVM: Add paravirt kvm_flush_tlb_others

On Tue, 2012-05-01 at 15:12 +0300, Avi Kivity wrote:
> We're now moving the freeing of kvm shadow page tables from using rcu to
> using an irq-protected scheme like gup_fast(), because of the
> performance differences.  We didn't track it down but I expect the cause
> is less reuse of cache-hot pages. 

It would be good to understand these things.. just doing things because
tends to come back and bite you :-)

If its cache behaviour you should be able to clearly see that using perf
stat.
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