Re: [Qemu-devel] [v2 1/2] docs: Add a doc about multiple compression threads

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Li Liang (liang.z.li@intel.com) wrote:
> Give some details about the multiple compression threads and how
> to use it in live migration.
> 
> Signed-off-by: Li Liang <liang.z.li@intel.com>
> ---
>  docs/multiple-compression-threads.txt | 128 ++++++++++++++++++++++++++++++++++
>  1 file changed, 128 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..a5e53de
> --- /dev/null
> +++ b/docs/multiple-compression-threads.txt

Should probably have migration in the title?

> +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
> +    Capabilities: ... compress: on
> +    ...
> +
> +TODO
> +====
> +Some faster compression/decompression method such as lz4 and quicklz
> +can help to reduce the CPU consumption when doing (de)compression.
> +Less (de)compression threads are needed when doing the migration.

OK, some high level questions:
   1) How does the performance compare to running a separate compressor
process in the stream rather than embedding it in the qemu?

   2) Since you're looking at different compression schemes do we need
something in the settings to select it, and to say what makes sense
for the 'compress_level'?   For example I don't know if lz4 or quicklz
have 1-10 for their compression levels?  How do I know which compression
schemes are available on any host?

Dave
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK