Re: [Qemu-devel] [PATCH] migration: use XBZRLE only after bulk stage

[Eric Blake <eblake@redhat.com>]

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On 03/01/2013 06:31 AM, Peter Lieven wrote:
> at the beginning of migration all pages are marked dirty and
> in the first round a bulk migration of all pages is performed.
> 
> currently all these pages are copied to the page cache regardless
> if there are frequently updated or not. this doesn't make sense
> since most of these pages are never transferred again.
> 
> this patch changes the XBZRLE transfer to only be used after
> the bulk stage has been completed. that means a page is added
> to the page cache the second time it is transferred and XBZRLE
> can benefit from the third time of transfer.
> 
> since the page cache is likely smaller than the number of pages
> its also likely that in the second round the page is missing in the
> cache due to collisions in the bulk phase.
> 
> on the other hand a lot of unneccssary mallocs, memdups and frees

s/unneccssary/unnecessary/

> are saved.
> 
> Signed-off-by: Peter Lieven <pl@kamp.de>

Do you have any benchmark numbers?  At any rate, the explanation seems
sound, so a benchmark should show this.

> ---
>  arch_init.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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