linux-kernel - Re: [PATCH 1/2] xen: enter/exit lazy_mmu_mode around m2p

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Date:	Tue, 27 Mar 2012 17:56:16 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>
Subject: Re: [PATCH 1/2] xen: enter/exit lazy_mmu_mode around m2p_override
 calls

On Tue, 27 Mar 2012, Konrad Rzeszutek Wilk wrote:
> On Tue, Mar 27, 2012 at 02:52:43PM +0100, Stefano Stabellini wrote:
> > This patch is a significant performance improvement for the
> 
> How much? 10%? 90%?

I think you are overestimating the meaning of "significant" :)

It is about 6% using grant_table and 2% using blkback.


> > m2p_override.
> 
> Can you explain what those calls do in the git commit description please?

Right, I have been way too concise.

Each m2p_add/remove_override call issues a MULTI_grant_table_op and a
__flush_tlb_single if kmap_op != NULL.
Batching all the calls together is a great performance benefit because
it means issuing one hypercall total rather than two hypercall per page.

I'll resend with a proper commit message.
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