[Bugs] [Bug 1558959] New: [brick-mux] incorrect event-thread scaling in server_reconfigure()

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1558959

            Bug ID: 1558959
           Summary: [brick-mux] incorrect event-thread scaling in
                    server_reconfigure()
           Product: GlusterFS
           Version: 4.0
         Component: core
          Assignee: mchangir at redhat.com
          Reporter: mchangir at redhat.com
                CC: amukherj at redhat.com, bugs at gluster.org,
                    moagrawa at redhat.com, rgowdapp at redhat.com
        Depends On: 1547888



+++ This bug was initially created as a clone of Bug #1547888 +++

Description of problem:
Whenever BRICK_ATTACH or BRICK_TERMINATE management operation is triggered on
the brick, glusterfs_autoscale_threads() scales the event-threads correctly.
However, the subsequent xlator_reconfigure()s that are invoked pass a default
value of "event-threads" option and value to server_reconfigure() causing a
rescaling of event-threads to 2. This is because the value of "event-threads"
option is always 1, presuming that the "server.event-threads" wasn't set to a
different value.

eg.
In case of brick-mux, event-threads are scaled by +1 for BRICK_ATTACH and
scaled by -1 for BRICK_TERMINATE. So starting with 5 bricks, if 5 more bricks
are added in a single operation, the brick receives 5 BRICK_ATTACH messages
causing the event-threads to be incrementally scaled to 10. However, the xlator
reconfigures that get invoked causes the system default value for
"event-thread" option to be used causing the scaling of event-threads back to
2.

This may cause an unwanted fop throttling at the bricks.
Care needs to be taken so that the event thread count is not reset after
rescaling at BRICK_ATTACH/BRICK_TERMINATE management op.

--- Additional comment from Worker Ant on 2018-03-09 16:21:48 IST ---

REVIEW: https://review.gluster.org/19689 (rpcsvc: correct event-thread scaling)
posted (#1) for review on master by Milind Changire

--- Additional comment from Worker Ant on 2018-03-12 14:19:13 IST ---

COMMIT: https://review.gluster.org/19689 committed in master by "Raghavendra G"
<rgowdapp at redhat.com> with a commit message- rpcsvc: correct event-thread
scaling

Problem:
Auto thread count derived from the number of attachs and detachs
was reset to 1 when server_reconfigure() was called.

Solution:
Avoid auto-thread-count reset to 1.

Change-Id: Ic00e86adb81ba3c828e354a6ccb638209ae58b3e
BUG: 1547888
Signed-off-by: Milind Changire <mchangir at redhat.com>


Referenced Bugs:

https://bugzilla.redhat.com/show_bug.cgi?id=1547888
[Bug 1547888] [brick-mux] incorrect event-thread scaling in
server_reconfigure()
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