[RFC PATCH 6/6] doc: Update multi-thread compression doc

[Zeyu Jin <jinzeyu@huawei.com>]

Modify the doc to fit the previous changes.

Signed-off-by: Zeyu Jin <jinzeyu@huawei.com>
Signed-off-by: Ying Fang <fangying1@huawei.com>
---
 docs/multi-thread-compression.txt | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/docs/multi-thread-compression.txt b/docs/multi-thread-compression.txt
index bb88c6bdf1..d429963cb0 100644
--- a/docs/multi-thread-compression.txt
+++ b/docs/multi-thread-compression.txt
@@ -33,14 +33,15 @@ 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.
+and you choose Zlib as compression method, 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.
+compression ratio. High compression ratio will take more time,
+level 1 stands for the best compression speed, and higher level means higher
+compression ration. For Zlib, users can select a level number between 0 and 9,
+where level 0 stands for no compression. For Zstd, users can select a
+level number between 1 and 22.
 
 
 When to use the multiple thread compression in live migration
@@ -116,16 +117,19 @@ to support the multiple thread compression migration:
 2. Activate compression on the source:
     {qemu} migrate_set_capability compress on
 
-3. Set the compression thread count on source:
+3. Set the compression method:
+    {qemu} migrate_set_parameter compress_method zstd
+
+4. Set the compression thread count on source:
     {qemu} migrate_set_parameter compress_threads 12
 
-4. Set the compression level on the source:
+5. Set the compression level on the source:
     {qemu} migrate_set_parameter compress_level 1
 
-5. Set the decompression thread count on destination:
+6. Set the decompression thread count on destination:
     {qemu} migrate_set_parameter decompress_threads 3
 
-6. Start outgoing migration:
+7. Start outgoing migration:
     {qemu} migrate -d tcp:destination.host:4444
     {qemu} info migrate
     Capabilities: ... compress: on
@@ -136,6 +140,7 @@ The following are the default settings:
     compress_threads: 8
     decompress_threads: 2
     compress_level: 1 (which means best speed)
+    compress_method: zlib
 
 So, only the first two steps are required to use the multiple
 thread compression in migration. You can do more if the default
@@ -143,7 +148,7 @@ 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
+Comparing to Zlib, 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.
-- 
2.23.0