The subject was discussed here:
https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg00206.html

This series is a solution for the issue with QMP monitor buffered input.
A JSON little parser is introduced to separate QMP commands read from the
input buffer so that incoming requests do not overwhelm the monitor queue.
A side effect raised in the test #247 was managed in the first patch.
It may be considered as a workaround. Any sane fix suggested will be
appreciated.

Note:
This series goes after the Vladimir's one:
'[PATCH v3 00/25] backup performance: block_status + async"'
To make the test #129 passed, the following patch should be applied first:
'[PATCH v3 01/25] iotests: 129 don't check backup "busy"'.

v2:
  02: The static JSONthrottle object was made a member of the Chardev structure.
      The fd_chr_read functions were merged.
      The monitor thread synchronization was added to protect the input queue
      from overflow.

Andrey Shinkevich (2):
  iotests: add another bash sleep command to 247
  monitor: increase amount of data for monitor to read

 chardev/char-fd.c          | 35 +++++++++++++++++++++++++++++++++--
 chardev/char-socket.c      | 42 +++++++++++++++++++++++++++++++++++++++---
 chardev/char.c             | 41 +++++++++++++++++++++++++++++++++++++++++
 include/chardev/char.h     | 15 +++++++++++++++
 monitor/monitor.c          |  2 +-
 tests/qemu-iotests/247     |  2 ++
 tests/qemu-iotests/247.out |  1 +
 7 files changed, 132 insertions(+), 6 deletions(-)

-- 
1.8.3.1

On 23.11.2020 18:44, Andrey Shinkevich wrote:
> The subject was discussed here:
> https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg00206.html
> 
> This series is a solution for the issue with QMP monitor buffered input.
> A JSON little parser is introduced to separate QMP commands read from the
> input buffer so that incoming requests do not overwhelm the monitor queue.
> A side effect raised in the test #247 was managed in the first patch.
> It may be considered as a workaround. Any sane fix suggested will be
> appreciated.
> 
> Note:
> This series goes after the Vladimir's one:
> '[PATCH v3 00/25] backup performance: block_status + async"'
> To make the test #129 passed, the following patch should be applied first:
> '[PATCH v3 01/25] iotests: 129 don't check backup "busy"'.
> 
> v2:
>    02: The static JSONthrottle object was made a member of the Chardev structure.
>        The fd_chr_read functions were merged.
>        The monitor thread synchronization was added to protect the input queue
>        from overflow.
> 
> Andrey Shinkevich (2):
>    iotests: add another bash sleep command to 247
>    monitor: increase amount of data for monitor to read
> 
>   chardev/char-fd.c          | 35 +++++++++++++++++++++++++++++++++--
>   chardev/char-socket.c      | 42 +++++++++++++++++++++++++++++++++++++++---
>   chardev/char.c             | 41 +++++++++++++++++++++++++++++++++++++++++
>   include/chardev/char.h     | 15 +++++++++++++++
>   monitor/monitor.c          |  2 +-
>   tests/qemu-iotests/247     |  2 ++
>   tests/qemu-iotests/247.out |  1 +
>   7 files changed, 132 insertions(+), 6 deletions(-)
> 


The Vladimir's modified test case

$ time (echo "{ 'execute': 'qmp_capabilities' }"; for i in {1..10000}; 
do echo "{ 'execute': 'query-block-jobs' } {"execute":"query-status"} { 
'execute': 'query-block-jobs' } {"execute":"query-status"}"; done; echo 
"{ 'execute': 'quit' }" ) | ./build/qemu-system-x86_64 -qmp stdio > 
/dev/null

shows the following performance

on master:
real	0m5.188s
user	0m5.310s
sys	0m2.539s

after the patch applied:
real	0m2.227s
user	0m2.483s
sys	0m0.480s

Andrey

On 23.11.2020 18:44, Andrey Shinkevich wrote:
> The subject was discussed here:
> https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg00206.html
> 
> This series is a solution for the issue with QMP monitor buffered input.
> A JSON little parser is introduced to separate QMP commands read from the
> input buffer so that incoming requests do not overwhelm the monitor queue.
> A side effect raised in the test #247 was managed in the first patch.
> It may be considered as a workaround. Any sane fix suggested will be
> appreciated.
> 
> Note:
> This series goes after the Vladimir's one:
> '[PATCH v3 00/25] backup performance: block_status + async"'
> To make the test #129 passed, the following patch should be applied first:
> '[PATCH v3 01/25] iotests: 129 don't check backup "busy"'.
> 
> v2:
>    02: The static JSONthrottle object was made a member of the Chardev structure.
>        The fd_chr_read functions were merged.
>        The monitor thread synchronization was added to protect the input queue
>        from overflow.
> 
> Andrey Shinkevich (2):
>    iotests: add another bash sleep command to 247
>    monitor: increase amount of data for monitor to read
> 
>   chardev/char-fd.c          | 35 +++++++++++++++++++++++++++++++++--
>   chardev/char-socket.c      | 42 +++++++++++++++++++++++++++++++++++++++---
>   chardev/char.c             | 41 +++++++++++++++++++++++++++++++++++++++++
>   include/chardev/char.h     | 15 +++++++++++++++
>   monitor/monitor.c          |  2 +-
>   tests/qemu-iotests/247     |  2 ++
>   tests/qemu-iotests/247.out |  1 +
>   7 files changed, 132 insertions(+), 6 deletions(-)
> 

...and with the extended number of QMP commands

time (echo "{ 'execute': 'qmp_capabilities' }"; for i in {1..10000}; do 
echo "{ 'execute': 'query-block-jobs' } {"execute":"query-status"} { 
'execute': 'query-block-jobs' } {"execute":"query-status"} { 'execute': 
'query-block-jobs' } {"execute":"query-status"} { 'execute': 
'query-block-jobs' } {"execute":"query-status"}"; done; echo "{ 
'execute': 'quit' }" ) | ./build/qemu-system-x86_64 -qmp stdio > /dev/null

on master:
real	0m10.112s
user	0m10.168s
sys	0m4.793s

after the patch applied:
real	0m4.140s
user	0m4.079s
sys	0m0.785s

Andrey