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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

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'll try.


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