[Qemu-devel] [PATCH RFC v2 0/4] block/qapi: refactor and optimize the qmp_query_blockstats()

[Dou Liyang <douly.fnst@cn.fujitsu.com>]

These patches aim to refactor the qmp_query_blockstats() and
improve the performance by reducing the running time of it.

qmp_query_blockstats() is used to monitor the blockstats, it
querys all the graph_bdrv_states or monitor_block_backends.

There are the two jobs:

1 For the performance:

1.1 the time it takes(ns) in each time:
the disk numbers     | 10    | 500
-------------------------------------
before these patches | 19429 | 667722 
after these patches  | 17516 | 557044

1.2 the I/O performance is degraded(%) during the monitor:

the disk numbers     | 10    | 500
-------------------------------------
before these patches | 1.3   | 14.2
after these patches  | 0.8   | 9.1

used the dd command likes this to test: 
dd if=date_1.dat of=date_2.dat conv=fsync oflag=direct bs=1k count=100k.

2 refactor qmp_query_blockstats():

From:

+--------------+      +---------------------+
 | 1            |      | 4.                  |
 |next_query_bds|      |bdrv_query_bds_stats +---+
 |              |      |                     |   |
 +--------^-----+      +-------------^-------+   |
          |                          |           |
+---------+----------+      +--------+-------+   |
| 0.                 |      | 2.             |   |
|qmp_query_blockstats+------>bdrv_query_stats<----
|                    |      |                |
+--------------------+      +--------+-------+
                                     |
                       +-------------v-------+
                       | 3.                  |
                       |bdrv_query_blk_stats |
                       |                     |
                       +---------------------+

To:

                                    +--------------+
                                    |              |
                           +--------v-----------+  |
                       +--->  3.                |  |
+-------------------+  |   |bdrv_query_bds_stats+--+
| 1.                +--+   |                    |
|                   +      +--------------------+
|qmp_query_blockstats--+
|                   |  |
+-------------------+  |   +--------------------+
                       |   | 2.                 |
                       +--->                    |
                           |bdrv_query_blk_stats|
                           |                    |
                           +--------------------+


Dou Liyang (4):
  block: refactor the bdrv_next_node and add some comments
  block/qapi: reduce the coupling between the bdrv_query_stats and
    bdrv_query_bds_stats
  block/qapi: acquire a reference instead of a lock during querying
    blockstats
  block/qapi: optimize the query function of the blockstats

 block.c      | 16 ++++++++---
 block/qapi.c | 92 +++++++++++++++++++++++++-----------------------------------
 2 files changed, 50 insertions(+), 58 deletions(-)

-- 
2.5.5