f0b8204072
As discussed at our nova meetings, reorganize the juno specs into three directories: - proposed: things proposed which weren't approved - approved: things we approved but didn't implement - implemented: things approved and implemented The first I suspect is the most controversial. I've done this because I worry about the case where a future developer wants to pick up something dropped by a previous developer, but has trouble finding previous proposed specifications on the topic. Note that the actual proposed specs for Juno are adding in a later commit. Change-Id: Idcf55ca37a83d7098dcb7c2971240c4e8fd23dc8
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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=====================================
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Create Nova Scheduler IO Ops Weighter
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=====================================
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https://blueprints.launchpad.net/nova/+spec/io-ops-weight
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Add a new nova scheduler weighter, sort the filter hosts according to host io
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ops number, aims to booting instances on light workload hosts.
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Problem description
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===================
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Currently, Nova scheduler can use host ram or metrics as hosts weight to choice
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host to booting instance, but have a large free ram host maybe have this many
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or more instances currently in build, resize, snapshot, migrate, rescue or
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unshelve task states, especially in some cases of the ram resource of compute
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hosts is very uneven. For example, We had two compute hosts, they had large
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enough free ram(hostA:64G and hostB:10G) to booting instances, by default Nova
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scheduler always choose hostA to booting instance and don't consider the
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concurrent instance task. The io_ops_filter can filter out the heavy workload
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hosts, but it can't help us to choose a most free compute host to booting.
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Using CONF.scheduler_host_subset_size can spread instances on suitable randomly
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compute hosts, but we think it's better that consider instance io ops as weight
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value.
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Proposed change
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===============
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Create a new scheduler weighter class 'IoOpsWeigher', use host_state.num_io_ops
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as weigh_object. Add a new CONF.io_ops_weight_multiplier, default value is
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-1.0.
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Alternatives
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------------
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None
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Data model impact
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-----------------
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None
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REST API impact
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---------------
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None
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Security impact
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---------------
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None
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Notifications impact
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--------------------
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None
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Other end user impact
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---------------------
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None
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Performance Impact
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------------------
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The new code itself will introduce some performance impact, new scheduler
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weighter 'IoOpsWeigher' add new calculation logic about hosts weight value.
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Direct use of the attribute 'num_io_ops' of HostState will not bring a big
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performance impact.
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Other deployer impact
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---------------------
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* Add a new weighter class 'IoOpsWeighter', it takes effect by default.
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* Add a new config option CONF.io_ops_weight_multiplier in nova.conf, default
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value is -1.0, positive numbers mean to prior choose heavy workload compute
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hosts.
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Developer impact
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----------------
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None
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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<kiwik-chenrui>
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Work Items
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----------
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* Add new weighter class 'IoOpsWeighter'.
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* Add some unit tests and tempest.
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Dependencies
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============
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None
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Testing
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=======
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New unit tests and tempest about 'IoOpsWeighter' will be added.
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Documentation Impact
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====================
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The docs about 'IoOpsWeighter' need to be drafted and new config option
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'io_ops_weight_multiplier' in nova.conf should be introduced, default value is
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-1.0, negative numbers mean to preference choose light workload compute hosts,
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positive numbers mean to the opposite thing.
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References
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==========
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None
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