Re: [Xen-devel] [PATCH V3 7/8] xen: switch to linear virtual mapped sparse p2m list
From: Konrad Rzeszutek Wilk
Date: Wed Nov 19 2014 - 15:39:16 EST
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
> >>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@xxxxxxxxxx>
> >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.
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