On 05/16/2012 05:59 AM, Orit Wasserman wrote: > Signed-off-by: Orit Wasserman <owass...@redhat.com> > --- > docs/xbzrle.txt | 97 > +++++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 files changed, 97 insertions(+), 0 deletions(-) > create mode 100644 docs/xbzrle.txt > > diff --git a/docs/xbzrle.txt b/docs/xbzrle.txt > new file mode 100644 > index 0000000..aafdb84 > --- /dev/null > +++ b/docs/xbzrle.txt > @@ -0,0 +1,97 @@ > +XBZRLE (Xor Based Zero Run Length Encoding) > +=========================================== > + > +Using XBZRLE (Xor Based Zero Run Length Encoding) allows for the reduction > of VM downtime > +and the total live-migration time of Virtual machines. It is particularly > useful for virtual machines running memory write intensive workloads that are > typical of large enterprise applications such as SAP ERP Systems, and > generally
Any reason you aren't wrapping at column 80?
> +speaking for any application that uses a sparse memory update pattern.
> +
> +Instead of sending the changed guest memory page this solution will send a
> compressed version of the updates, thus reducing the amount of data sent
> during live migration.
> +In order to be able to calculate the update, the previous memory pages
> needed to be stored. Those pages are stored in a dedicated cache (hash table)
> and are accessed by their address.
> +The larger the cache size the better the chances are that the page has
> already been stored in the cache. A Small cache size will result in high
> cache miss rate.
s/Small/small/
> +Usage
> +======
> +
> +1. Activate xbzrle
> +2. Set the XBZRLE cache size - the cache size is in MBytes and should be a
> power of 2. The cache default value is 64MBytes.
> +3. start outgoing migration
> +
> +A typical usage scenario:
> + {qemu} migrate_set_parameter xbzrle
> + {qemu} migrate_set_cachesize 256m
> + {qemu} migrate -d tcp:destination.host:4444
> + {qemu} info migrate
> + ...
> + transferred ram-duplicate: A kbytes
> + transferred ram-normal: B kbytes
> + transferred ram-xbrle: C kbytes
> + overflow ram-xbrle: D pages
> + cache-miss ram-xbrle: E pages
> +
> +cache-miss: the number of cache misses to date - high cache-miss rate
> +indicates that the cache size is set too low.
> +overflow: the number of overflows in the decoding which where the delta
> could not be compressed. This can happen if the changes in the pages are too
> large
> +or there are many short changes for example change every second byte (half a
> page).
Can cachesize be modified during an in-progress migration? Do both
source and destination need to agree on cache size?
--
Eric Blake ebl...@redhat.com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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