mirror of
https://gitlab.com/qemu-project/qemu
synced 2024-11-05 20:35:44 +00:00
docs: Add a doc about multiple thread compression
Give some details about the multiple thread (de)compression and how to use it in live migration. Signed-off-by: Liang Li <liang.z.li@intel.com> Signed-off-by: Yang Zhang <yang.z.zhang@intel.com> Reviewed-by: Dr.David Alan Gilbert <dgilbert@redhat.com> Reviewed-by: Juan Quintela <quintela@redhat.com> Signed-off-by: Juan Quintela <quintela@redhat.com>
This commit is contained in:
Liang Li
Juan Quintela
parent
38003aee19
commit
263170e679
1 changed files with 149 additions and 0 deletions
149
docs/multi-thread-compression.txt
Normal file
149
docs/multi-thread-compression.txt
Normal file
|
|
@ -0,0 +1,149 @@
|
|||
Use multiple thread (de)compression in live migration
|
||||
=====================================================
|
||||
Copyright (C) 2015 Intel Corporation
|
||||
Author: Liang Li <liang.z.li@intel.com>
|
||||
|
||||
This work is licensed under the terms of the GNU GPLv2 or later. See
|
||||
the COPYING file in the top-level directory.
|
||||
|
||||
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
|
||||
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 total migration time can also be reduced
|
||||
about 70% in a typical case. In addition to this, the VM downtime can be
|
||||
reduced about 50%. The benefit depends on data's compressibility in VM.
|
||||
|
||||
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 decrease; this factor can reduce
|
||||
the total migration time. If the process of the compression is quick
|
||||
enough, then the total migration time can be reduced, and multiple
|
||||
thread compression can be used to accelerate the compression process.
|
||||
|
||||
The decompression speed of Zlib is at least 4 times as quick as
|
||||
compression, if the source and destination CPU have equal speed,
|
||||
keeping the compression thread count 4 times the decompression
|
||||
thread count can avoid resource 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 thread compression in live migration
|
||||
=============================================================
|
||||
Compression of data will consume extra CPU cycles; so 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 of
|
||||
multiple thread compression will be very helpful. If both the CPU and
|
||||
the network bandwidth are adequate, use of multiple thread compression
|
||||
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: RHEL 6.5 64-bit
|
||||
Parameter: qemu-system-x86_64 -enable-kvm -smp 4 -m 4096
|
||||
/share/ia32e_rhel6u5.qcow -monitor stdio
|
||||
|
||||
There is no additional application is running on the guest when doing
|
||||
the test.
|
||||
|
||||
|
||||
Speed limit: 1000Gb/s
|
||||
---------------------------------------------------------------
|
||||
| original | compress thread: 8
|
||||
| way | decompress thread: 2
|
||||
| | compression level: 1
|
||||
---------------------------------------------------------------
|
||||
total time(msec): | 3333 | 1833
|
||||
---------------------------------------------------------------
|
||||
downtime(msec): | 100 | 27
|
||||
---------------------------------------------------------------
|
||||
transferred ram(kB):| 363536 | 107819
|
||||
---------------------------------------------------------------
|
||||
throughput(mbps): | 893.73 | 482.22
|
||||
---------------------------------------------------------------
|
||||
total ram(kB): | 4211524 | 4211524
|
||||
---------------------------------------------------------------
|
||||
|
||||
There is an application running on the guest which write random numbers
|
||||
to RAM block areas periodically.
|
||||
|
||||
Speed limit: 1000Gb/s
|
||||
---------------------------------------------------------------
|
||||
| original | compress thread: 8
|
||||
| way | decompress thread: 2
|
||||
| | compression level: 1
|
||||
---------------------------------------------------------------
|
||||
total time(msec): | 37369 | 15989
|
||||
---------------------------------------------------------------
|
||||
downtime(msec): | 337 | 173
|
||||
---------------------------------------------------------------
|
||||
transferred ram(kB):| 4274143 | 1699824
|
||||
---------------------------------------------------------------
|
||||
throughput(mbps): | 936.99 | 870.95
|
||||
---------------------------------------------------------------
|
||||
total ram(kB): | 4211524 | 4211524
|
||||
---------------------------------------------------------------
|
||||
|
||||
Usage
|
||||
=====
|
||||
1. Verify both the source and destination QEMU are able
|
||||
to support the multiple thread compression migration:
|
||||
{qemu} info_migrate_capabilities
|
||||
{qemu} ... compress: off ...
|
||||
|
||||
2. Activate compression on the source:
|
||||
{qemu} migrate_set_capability compress on
|
||||
|
||||
3. Set the compression thread count on source:
|
||||
{qemu} migrate_set_parameter compress_threads 12
|
||||
|
||||
4. Set the compression level on the source:
|
||||
{qemu} migrate_set_parameter compress_level 1
|
||||
|
||||
5. Set the decompression thread count on destination:
|
||||
{qemu} migrate_set_parameter decompress_threads 3
|
||||
|
||||
6. Start outgoing migration:
|
||||
{qemu} migrate -d tcp:destination.host:4444
|
||||
{qemu} info migrate
|
||||
Capabilities: ... compress: on
|
||||
...
|
||||
|
||||
The following are the default settings:
|
||||
compress: off
|
||||
compress_threads: 8
|
||||
decompress_threads: 2
|
||||
compress_level: 1 (which means best speed)
|
||||
|
||||
So, only the first two steps are required to use the multiple
|
||||
thread compression in migration. You can do more if the default
|
||||
settings are not appropriate.
|
||||
|
||||
TODO
|
||||
====
|
||||
Some faster (de)compression method such as LZ4 and Quicklz can help
|
||||
to reduce the CPU consumption when doing (de)compression. If using
|
||||
these faster (de)compression method, less (de)compression threads
|
||||
are needed when doing the migration.
|
||||
Loading…
Reference in a new issue