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

[Eric Blake]

On 11/06/2014 12:08 PM, Li Liang wrote:
> Give some details about the multiple compression threads and how
> to use it in live migration.
> 
> Signed-off-by: Li Liang <address@hidden>
> ---
>  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
> @@ -0,0 +1,128 @@
> +Use multiple (de)compression threads in live migration
> +=================================================================
> +Copyright (C) 2014 Li Liang <address@hidden>

Asserting copyright without also mentioning an open license is awkward
in open source (IANAL, but as I understand it, in some areas, asserting
a copyright without also granting disclaimers merely gets the default
non-open status where the file cannot be copied at all; the license is
essential to make it obvious that the copyright holder INTENDS for the
file to be copied in some circumstances).  Thus, you need to explicitly
call out GPLv2+ (even if it can be argued it is was implied by the
top-level LICENSE) or some other compatible license to be safe.

> +
> +
> +Contents:
> +=========
> +* Introduction
> +* When to use
> +* Performance
> +* Usage
> +* TODO
> +
> +Introduction
> +============
> +Instead of sending the guest memory directly, this solution will
> +compress the ram page before sending, after receiving, the data will

s/sending,/sending;/

> +be decompressed. Using compression in live migration can help
> +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
> +70% in a typical case.
> +
> +The process of compression will consume additional CPU cycles, and the
> +extra CPU cycles will increase the migration time. On the other hand,
> +the amount of data transferred will reduced, this factor can reduce
> +the migration time. If the process of the compression is quick
> +enough, then the total migration time can be reduced, and multiple
> +compression threads can be used to accelerate the compression process.
> +
> +The decompression speed of zlib is at least 4 times as quickly as

s/quickly/quick/

> +compression, if the source and destination CPU have equal speed,
> +keeping the compression thread count 4 times the decompression
> +thread count can avoid CPU waste.
> +
> +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

s/lot of//
s/cycles,/cycles; so/

> +with high overhead of CPU, avoid using this feature. When the network
> +bandwidth is very limited and the CPU resource is adequate, use the

s/use the/use of/

> +multiple compression threads will be very helpful. If both the CPU and
> +the network bandwidth are adequate, use multiple compression threads

s/use/use of/

> +can still help to reduce the migration time.
> +
> +Performance
> +===========
> +Test environment:
> +
> +CPU: Intel(R) Xeon(R) CPU E5-2680 0 @ 2.70GHz
> +Socket Count: 2
> +Ram: 128G
> +NIC: Intel I350 (10/100/1000Mbps)
> +Host OS: CentOS 7 64-bit
> +Guest OS: Ubuntu 12.10 64-bit
> +Parameter: qemu-system-x86_64 -enable-kvm -m 1024
> + /share/ia32e_ubuntu12.10.img -monitor stdio
> +
> +There is no additional application is running on the guest when doing
> +the test.
> +
> +
> +Speed limit: 32MB/s
> +---------------------------------------------------------------
> +                    | original  | compress thread: 8
> +                    |   way     | decompress thread: 2
> +                    |           | compression level: 1
> +---------------------------------------------------------------
> +total time(msec):   |  26561    |  7920
> +---------------------------------------------------------------
> +transferred ram(kB):|  877054   | 260641
> +---------------------------------------------------------------
> +throughput(mbps):   |  270.53   | 269.68
> +---------------------------------------------------------------
> +total ram(kB):      |  1057604  | 1057604
> +---------------------------------------------------------------
> +
> +
> +Speed limit: No
> +---------------------------------------------------------------
> +                    | original  | compress thread: 15
> +                    |   way     | decompress thread: 4
> +                    |           | compression level: 1
> +---------------------------------------------------------------
> +total time(msec):   |  7611     |  2888
> +---------------------------------------------------------------
> +transferred ram(kB):|  876761   | 262301
> +---------------------------------------------------------------
> +throughput(mbps):   |  943.78   | 744.27
> +---------------------------------------------------------------
> +total ram(kB):      |  1057604  | 1057604
> +---------------------------------------------------------------
> +
> +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.
> 

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

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