Reviewed: https://review.opendev.org/713863
Committed:
https://git.openstack.org/cgit/openstack/nova/commit/?id=5ab9ef11e27014ce8b43e1bac76903fed70d0fbf
Submitter: Zuul
Branch: master
commit 5ab9ef11e27014ce8b43e1bac76903fed70d0fbf
Author: Johannes Kulik <johannes.ku...@sap.com>
Date: Thu Mar 19 12:51:25 2020 +0100
Don't recompute weighers' minval/maxval attributes
Changing the minval/maxval attribute to the minimum/maxium of every
weigher run changes the outcome of future runs. We noticed it in the
SoftAffinityWeigher, where a previous run with a host hosting a lot of
instances for a server-group would make a later run use that maximum.
This resulted in the weight being lower than 1 for a host hosting all
instances of another server-group, if the number of instances of that
server-group on that host is less than a previous server-group's
instances on any host.
Previously, there were two places that computed the maxval/minval - once
in normalize() and once in weigh_objects() - but only the one in
weigh_objects() saved the values to the weigher.
The code now uses the maxval/minval as defined by the weigher and keeps
the weights inside the maxval-minval range. There's also only one place
to compute the minval/maxval now, if the weigher did not set a value:
normalize().
Closes-Bug: 1870096
Change-Id: I60a90dabcd21b4e049e218c7c55fa075bb7ff933
** Changed in: nova
Status: In Progress => Fix Released
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https://bugs.launchpad.net/bugs/1870096
Title:
soft-affinity weight not normalized base on server group's maximum
Status in OpenStack Compute (nova):
Fix Released
Status in OpenStack Compute (nova) pike series:
New
Status in OpenStack Compute (nova) queens series:
New
Status in OpenStack Compute (nova) rocky series:
New
Status in OpenStack Compute (nova) stein series:
New
Status in OpenStack Compute (nova) train series:
New
Bug description:
Description
===========
When using soft-affinity to schedule instances on the same host, the
weight is unexpectedly low if a server was previously scheduled to any
server-group with more members on a host. This low weight can then be
easily outweighed by differences in resources (e.g. RAM/CPU).
Steps to reproduce
==================
Do not restart nova-scheduler in the process or the bug doesn't
appear. You need to change the ServerGroupSoftAffinityWeigher to
actually log the weights it computes to see the problem.
* Create a server-group with soft-affinity (let's call it A)
* Create 6 servers in server-group A, one after the other so they end up on
the same host.
* Create another server-group with soft-affinity (B)
* Create 1 server in server-group B
* Create 1 server in server-group B and look at the scheduler's weights
assigned to the hosts by the ServerGroupSoftAffinityWeigher.
Expected result
===============
The weight assigned to the host by the ServerGroupSoftAffinityWeigher
should be 1, as the maximum number of instances for server-group B is
on that host (the one we created there before).
Actual result
=============
The weight assigned to the host by the ServerGroupSoftAffinityWeigher is 0.2,
as the maximum number of instances ever encountered on a host is 5.
Environment
===========
We noticed this on a queens version of nova a year ago. Can't give the
exact commit anymore, but the code still looks broken in current
master.
I've opened a review-request for fixing this bug here:
https://review.opendev.org/#/c/713863/
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