Re: [Qemu-devel] [PATCHv2 9/9] migration: use XBZRLE only after bulk stage

[Eric Blake <eblake@redhat.com>]

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On 03/15/2013 09:50 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.
> 
> the following results have been taken earlier while executing
> the test program from docs/xbzrle.txt. (+) with the patch and (-)
> without. (thanks to Eric Blake for reformatting and comments)

Hey - I know that guy :)

> 
> + total time: 22185 milliseconds
> - total time: 22410 milliseconds
> 
> Shaved 0.3 seconds, better than 1%!
> 
> + downtime: 29 milliseconds
> - downtime: 21 milliseconds
> 
> Not sure why downtime seemed worse, but probably not the end of the world.
> 
> + transferred ram: 706034 kbytes
> - transferred ram: 721318 kbytes
> 
> Fewer bytes sent - good.
> 
> + remaining ram: 0 kbytes
> - remaining ram: 0 kbytes
> + total ram: 1057216 kbytes
> - total ram: 1057216 kbytes
> + duplicate: 108556 pages
> - duplicate: 105553 pages
> + normal: 175146 pages
> - normal: 179589 pages
> + normal bytes: 700584 kbytes
> - normal bytes: 718356 kbytes
> 
> Fewer normal bytes...
> 
> + cache size: 67108864 bytes
> - cache size: 67108864 bytes
> + xbzrle transferred: 3127 kbytes
> - xbzrle transferred: 630 kbytes
> 
> ...and more compressed pages sent - good.
> 
> + xbzrle pages: 117811 pages
> - xbzrle pages: 21527 pages
> + xbzrle cache miss: 18750
> - xbzrle cache miss: 179589
> 
> And very good improvement on the cache miss rate.
> 
> + xbzrle overflow : 0
> - xbzrle overflow : 0
> 
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
>  arch_init.c |    2 +-
>  1 file changed, 1 insertion(+), 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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