Re: [Qemu-devel] [PATCH RFC v3 0/2] block/qapi: refactor and optimize the qmp_query_blockstats()

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Wed, Jan 04, 2017 at 02:58:09PM +0800, Dou Liyang wrote:
> Change log v2 -> v3:
>  1. Remove the unnecessary code for the bdrv_next_node().
>  2. Remove the change of the locking rules.
>     Even if this change can improve the performance, but it may
>     effect the consistency.
> 
> For the multi-disks guest, we can use the dataplane feature to
> hold performance does not drop, if we execute some slow monitor
> commands, such as "info blockstats". But, without this feature, 
> How to reduce the decline in performance?
> 
> These patches aim to refactor the qmp_query_blockstats() and
> improve the performance by reducing the running time of it.
> 
> 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  | 18536 | 627945
> 
> 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  | 1.0   | 11.3
> 
> 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 (2):
>   block/qapi: reduce the coupling between the bdrv_query_stats and
>     bdrv_query_bds_stats
>   block/qapi: reduce the execution time of qmp_query_blockstats
> 
>  block/qapi.c | 94 ++++++++++++++++++++++++++----------------------------------
>  1 file changed, 40 insertions(+), 54 deletions(-)

Leaving review to Markus Armbruster since he maintains this area.

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