linux-kernel - Re: [PATCH v12 06/18] xen/pvh: MMU changes for PVH (v2)

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Message-ID: <52C68D73.70005@citrix.com>
Date:	Fri, 3 Jan 2014 10:14:11 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Mukesh Rathor <mukesh.rathor@...cle.com>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	<linux-kernel@...r.kernel.org>, <xen-devel@...ts.xenproject.org>,
	<boris.ostrovsky@...cle.com>, <stefano.stabellini@...citrix.com>
Subject: Re: [PATCH v12 06/18] xen/pvh: MMU changes for PVH (v2)

On 03/01/14 01:36, Mukesh Rathor wrote:
> On Thu, 2 Jan 2014 11:24:50 +0000
> David Vrabel <david.vrabel@...rix.com> wrote:
> 
>> On 01/01/14 04:35, Konrad Rzeszutek Wilk wrote:
>>> From: Mukesh Rathor <mukesh.rathor@...cle.com>
>>>
>>> .. which are surprinsingly small compared to the amount for PV code.
>>>
>>> PVH uses mostly native mmu ops, we leave the generic (native_*) for
>>> the majority and just overwrite the baremetal with the ones we need.
>>>
>>> We also optimize one - the TLB flush. The native operation would
>>> needlessly IPI offline VCPUs causing extra wakeups. Using the
>>> Xen one avoids that and lets the hypervisor determine which
>>> VCPU needs the TLB flush.
>>
>> This TLB flush optimization should be a separate patch.
> 
> It's not really an "optimization", we are using PV mechanism instead
> of native because PV one performs better.

Um.  Isn't that the very definition of an optimization?

I do think it is better for the essential MMU changes to be clearly
separate from the optional ones.

David

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