[Qemu-devel] [PATCH 2/2] docs: Add a document about multiple compression threads

[Liliang]

From: Li Liang <address@hidden>

Give some details about how to use the multiple compress threads feature
in live migration.

Signed-off-by: Li Liang <address@hidden>
---
 docs/multiple-compression-threads.txt | 57 +++++++++++++++++++++++++++++++++++
 1 file changed, 57 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..83e9e5b
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+++ b/docs/multiple-compression-threads.txt
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+Use multiple compression(decompression) threads in live migration
+=================================================================
+Instead of sending the guest memory directly, this solution will
+compress the ram page before sending, after receiving, the data how to
+us 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
+80% in a typical case.
+
+The process of compression will consume additional CPU cycles, and the
+extra CPU cycles will increase the migration time. In another hand,
+the amount of data transferred will reduced, this factor can reduce
+the migration time. If the process of the compression is quickly
+enough, then the total migration time can be reduced, multiple
+compression threads can be used to accelerate the compression process.
+
+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.
+
+
+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
+    Capablilties: ... compress: on
+    ...
-- 
1.9.1