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 <liang.z...@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 > @@ -0,0 +1,128 @@ > +Use multiple (de)compression threads in live migration > +================================================================= > +Copyright (C) 2014 Li Liang <liang.z...@intel.com>
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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