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

[Li, Liang Z]

This is a RFC version.

-----Original Message-----
From: Li, Liang Z 
Sent: Friday, October 31, 2014 1:40 PM
To: address@hidden
Cc: address@hidden; address@hidden; address@hidden; Li, Liang Z
Subject: [PATCH 2/2] docs: Add a document about multiple compression threads

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
--- /dev/null
+++ b/docs/multiple-compression-threads.txt
@@ -0,0 +1,57 @@
+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