Re: [Xen-devel] slow live magration / xc_restore on xen4 pvops

[Brendan Cully <Brendan@xxxxxxxxx>]

On Thursday, 03 June 2010 at 06:47, Keir Fraser wrote:
> On 03/06/2010 02:04, "Brendan Cully" <Brendan@xxxxxxxxx> wrote:
> 
> > I've done a bit of profiling of the restore code and observed the
> > slowness here too. It looks to me like it's probably related to
> > superpage changes. The big hit appears to be at the front of the
> > restore process during calls to allocate_mfn_list, under the
> > normal_page case. It looks like we're calling
> > xc_domain_memory_populate_physmap once per page here, instead of
> > batching the allocation? I haven't had time to investigate further
> > today, but I think this is the culprit.
> 
> Ccing Edwin Zhai. He wrote the superpage logic for domain restore.

Here's some data on the slowdown going from 2.6.18 to pvops dom0:

I wrapped the call to allocate_mfn_list in uncanonicalize_pagetable
to measure the time to do the allocation.

kernel, min call time, max call time
2.6.18, 4 us, 72 us
pvops, 202 us, 10696 us (!)

It looks like pvops is dramatically slower to perform the
xc_domain_memory_populate_physmap call!

I'll attach the patch and raw data below.

Attachment: alloc-profile.diff
Description: Text document

Attachment: 2.6.18-alloc
Description: Text document

Attachment: pvops-alloc
Description: Text document

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