[dm-devel] [PATCH v6 0/1] multipath-tools: Prioritizer based on a latency algorithm

[Yang Feng]

This patch value is in the following: 
1. In the Storage-Backup environment of HyperCluster, includes
one storage array near to the host and one remote storage array,
and the two storage arrays have the same hardware. The same LUN is
writed or readed by the two storage arrays. However, usually, the
average latency of the paths of the remote storage array is higher
than the near storage array's. Apparently, the prioritizer can be
a good automatic solution. And the current selectors don't solve it,
IOs will send to the paths of the remote storage array, IOPS will
be influenced unavoidably.

2. In the environment of single storage array, the prioritizer can
automatically separate the paths who's latency is higher, IOs will
not send to this paths. But the current selectors don't solve this
problem, IOPS will be influenced unavoidably.

Changes from v5:
* Max average latency value is set to 100s, and min value is set to
1us. Use logarithmic scale to partition different path priority ranks
instead of linear scale, while use args "base_num" instead of
"latency_interval". Fix according to Martin's reviews.
* Make log to be more regular. Fix according to Martin's reviews.

Changes from v4:
* Args "latency_interval" is set by using logarithmic scale, 
where base number is 10. Fix according to Martin's reviews.
* The value of "MAX_LATENCY_INTERVAL" is set 10 from 60.

Changes from v3:
* Delete Copyright time "2021", Fix according to Xose's reviews.
* Add version for GPL, Fix according to Xose's reviews.

Changes from v2:
* Reorganize the commit comment and patch format.
* Added Benjamin, Martin and Xose's Reviewed-by.

Changes from v1:
* The value of "MIN_IO_NUM" is set 2 from 10.
* Fix according to Benjamin, Martin and Xose's reviews.

Yang Feng (1):
  multipath-tools: Prioritizer based on a latency algorithm

 libmultipath/prio.h                      |   1 +
 libmultipath/prioritizers/Makefile       |   4 +
 libmultipath/prioritizers/path_latency.c | 257 +++++++++++++++++++++++++++++++
 multipath/multipath.conf.5               |  20 +++
 4 files changed, 282 insertions(+)
 create mode 100644 libmultipath/prioritizers/path_latency.c

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2.6.4.windows.1