Re: [Qemu-devel] [PATCH 2/2] docs: Add a document about multiple compression threads

[Eric Blake]

On 10/31/2014 06:40 AM, Liliang wrote:
> From: Li Liang <address@hidden>
> 
> Give some details about how to use the multiple compress threads feature
> in live migration.
> 
> Signed-off-by: Li Liang <address@hidden>
> ---
>  docs/multiple-compression-threads.txt | 57 
> +++++++++++++++++++++++++++++++++++
>  1 file changed, 57 insertions(+)
>  create mode 100644 docs/multiple-compression-threads.txt
> 
> diff --git a/docs/multiple-compression-threads.txt 
> b/docs/multiple-compression-threads.txt
> new file mode 100644
> index 0000000..83e9e5b
> --- /dev/null
> +++ b/docs/multiple-compression-threads.txt
> @@ -0,0 +1,57 @@
> +Use multiple compression(decompression) threads in live migration

Missing a copyright notice (yeah, not all files in our docs directory
are good examples, but we're starting to get better at it).

> +=================================================================
> +Instead of sending the guest memory directly, this solution will
> +compress the ram page before sending, after receiving, the data how to
> +us will be decompressed. Using compression in live migration can help

s/how to us will be/has to be/ ?

> +to reduce the data transferred about 60%, this is very useful when the
> +bandwidth is limited, and the migration time can also be reduced about
> +80% in a typical case.

What network bandwidth did you have in your tests?  I suspect that the
speedups you saw may be more pronounced on low-bandwidth links, and that
you would be wise to give more details about reproducing your test
setup, since not everyone will see the same speedups.

> +
> +The process of compression will consume additional CPU cycles, and the
> +extra CPU cycles will increase the migration time. In another hand,

s/In another/On the other/

> +the amount of data transferred will reduced, this factor can reduce
> +the migration time. If the process of the compression is quickly

s/quickly/quick/

> +enough, then the total migration time can be reduced, multiple

s/multiple/and multiple/

> +compression threads can be used to accelerate the compression process.
> +
> +Compression level can be used to control the compression speed and the
> +compression ratio. High compression ratio will take more time, level 0
> +stands for no compression, level 1 stands for the best compression
> +speed,and level 9 stands for the best compression ratio. Users can
> +select a level number between 0 and 9.
> +
> +
> +When to use the multiple compression threads in live migration
> +==============================================================
> +Compression of data will consume lot of extra CPU cycles, in a system
> +with high overhead of CPU, avoid using this feature. When the network
> +bandwidth is very limited and the CPU resource is adequate, use the
> +multiple compression threads will be very helpful. If both the CPU and
> +the network bandwidth are adequate, use multiple compression threads
> +can still help to reduce the migration time.
> +
> +
> +Usage
> +======
> +1. Verify the destination QEMU version is able to support the multiple
> +compression threads migration:
> +    {qemu} info_migrate_capablilites
> +    {qemu} ... compress: off ...
> +
> +2. Activate compression on the souce:
> +    {qemu} migrate_set_capability compress on
> +
> +3. Set the compression thread count on source:
> +    {qemu} migrate_set_compress_threads 10
> +
> +4. Set the compression level on the source:
> +    {qemu} migrate_set_compress_level 1
> +
> +5. Set the decompression thread count on destination:
> +    {qemu} migrate_set_decompress_threads 5
> +
> +6. Start outgoing migration:
> +    {qemu} migrate -d tcp:destination.host:4444
> +    {qemu} info migrate
> +    Capablilties: ... compress: on

s/Capablilties/Capabilities/

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

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