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

[Li Liang <liang.z.li@intel.com>]

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
@@ -0,0 +1,128 @@
+Use multiple (de)compression threads in live migration
+=================================================================
+Copyright (C) 2014 Li Liang <liang.z.li@intel.com>
+
+
+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 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
+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
+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.
+
+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.
-- 
1.9.1