linux-kernel - Re: [Xen-devel] [PATCH V3 7/8] xen: switch to linear virtual mapped sparse p2m list

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Date:	Thu, 13 Nov 2014 10:21:01 +0100
From:	Juergen Gross <jgross@...e.com>
To:	David Vrabel <david.vrabel@...rix.com>,
	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	konrad.wilk@...cle.com, boris.ostrovsky@...cle.com, x86@...nel.org,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com
Subject: Re: [Xen-devel] [PATCH V3 7/8] xen: switch to linear virtual mapped
 sparse p2m list

On 11/11/2014 06:47 PM, David Vrabel wrote:
> On 11/11/14 05:43, Juergen Gross wrote:
>> At start of the day the Xen hypervisor presents a contiguous mfn list
>> to a pv-domain. In order to support sparse memory this mfn list is
>> accessed via a three level p2m tree built early in the boot process.
>> Whenever the system needs the mfn associated with a pfn this tree is
>> used to find the mfn.
>>
>> Instead of using a software walked tree for accessing a specific mfn
>> list entry this patch is creating a virtual address area for the
>> entire possible mfn list including memory holes. The holes are
>> covered by mapping a pre-defined  page consisting only of "invalid
>> mfn" entries. Access to a mfn entry is possible by just using the
>> virtual base address of the mfn list and the pfn as index into that
>> list. This speeds up the (hot) path of determining the mfn of a
>> pfn.
>>
>> Kernel build on a Dell Latitude E6440 (2 cores, HT) in 64 bit Dom0
>> showed following improvements:
>>
>> Elapsed time: 32:50 ->  32:35
>> System:       18:07 ->  17:47
>> User:        104:00 -> 103:30
>>
>> Tested on 64 bit dom0 and 32 bit domU.
>
> Reviewed-by: David Vrabel <david.vrabel@...rix.com>
>
> Can you please test this with the following guests/scenarios.
>
> * 64 bit dom0 with PCI devices with high MMIO BARs.

I'm not sure I have a machine available with this configuration.

> * 32 bit domU with PCI devices assigned.
> * 32 bit domU with 64 GiB of memory.
> * domU that starts pre-ballooned and is subsequently ballooned up.
> * 64 bit domU that is saved and restored (or local host migration)
> * 32 bit domU that is saved and restored (or local host migration)

I'll try.


Juergen
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