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

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Date:	Wed, 19 Nov 2014 15:38:48 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Juergen Gross <jgross@...e.com>
Cc:	David Vrabel <david.vrabel@...rix.com>,
	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.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 Thu, Nov 13, 2014 at 10:21:01AM +0100, Juergen Gross wrote:
> 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 would also add: try 64-bit domU with really bizzare memory sizes that
are not odd. Like 9765431 or such. And naturally do the migration to
make sure that the re-hook doesn't miss a page or such.

> 
> I'll try.
> 
> 
> Juergen
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