Public bug reported: Observed on ironic multinode grenade job (using Ocata scheduler).
Ironic returns its nodes in the same relative order (by internal DB id). Quite often (and in DevStack always by default) ironic nodes are identical, thus filter scheduler gives them the same weight. As a result, during concurrent requests to schedule instances, the weighed_hosts list goes always in the same order and is being always consumed from the start. This leads to the first node selected often enough to exceed the default number of retries when it is being stolen by another concurrent request (as it also always picks the first one from the list). See log examples from the same gate job [0-2], failure [3] (ServerActionsTestJSON test failure). Notice how the weighed hosts list is always is always in the same order, and scheduler retries 3 times on nodes that are being already occupied by another parallel request, always picking the currently first one. This could be fixed by increasing the host_subset_size config option from its default value of 1, which would bring some randomness to the first element. While fine (and actually recommended) for baremetal-only case, this choice is a bit suboptimal in a mixed hypervizor (virtual+ironic computes) as it makes scheduling logic for virtual computes less ideal. Instead, it might be better to always randomize the first hosts in the weighed_hosts list for hosts with identical (and maximal) weight as those should be equally good candidates to schedule to. This will decrease collision and rescheduling chances, definitely for ironic nodes, but also to some tiny extent for standard compute hosts as well. [0] http://logs.openstack.org/12/493812/2/check/gate-grenade-dsvm-ironic-multinode-multitenant-ubuntu-xenial/8d3f840/logs/old/screen-n-sch.txt.gz#_2017-08-15_13_27_29_410 [1] http://logs.openstack.org/12/493812/2/check/gate-grenade-dsvm- ironic-multinode-multitenant-ubuntu- xenial/8d3f840/logs/old/screen-n-sch.txt.gz#_2017-08-15_13_27_31_839 [2] http://logs.openstack.org/12/493812/2/check/gate-grenade-dsvm- ironic-multinode-multitenant-ubuntu- xenial/8d3f840/logs/old/screen-n-sch.txt.gz#_2017-08-15_13_27_34_244 [3] http://logs.openstack.org/12/493812/2/check/gate-grenade-dsvm- ironic-multinode-multitenant-ubuntu- xenial/8d3f840/logs/testr_results.html.gz ** Affects: nova Importance: Undecided Assignee: Pavlo Shchelokovskyy (pshchelo) Status: In Progress ** Tags: ironic scheduler -- You received this bug notification because you are a member of Yahoo! Engineering Team, which is subscribed to OpenStack Compute (nova). https://bugs.launchpad.net/bugs/1711184 Title: scheduler selects the same ironic node several times Status in OpenStack Compute (nova): In Progress Bug description: Observed on ironic multinode grenade job (using Ocata scheduler). Ironic returns its nodes in the same relative order (by internal DB id). Quite often (and in DevStack always by default) ironic nodes are identical, thus filter scheduler gives them the same weight. As a result, during concurrent requests to schedule instances, the weighed_hosts list goes always in the same order and is being always consumed from the start. This leads to the first node selected often enough to exceed the default number of retries when it is being stolen by another concurrent request (as it also always picks the first one from the list). See log examples from the same gate job [0-2], failure [3] (ServerActionsTestJSON test failure). Notice how the weighed hosts list is always is always in the same order, and scheduler retries 3 times on nodes that are being already occupied by another parallel request, always picking the currently first one. This could be fixed by increasing the host_subset_size config option from its default value of 1, which would bring some randomness to the first element. While fine (and actually recommended) for baremetal-only case, this choice is a bit suboptimal in a mixed hypervizor (virtual+ironic computes) as it makes scheduling logic for virtual computes less ideal. Instead, it might be better to always randomize the first hosts in the weighed_hosts list for hosts with identical (and maximal) weight as those should be equally good candidates to schedule to. This will decrease collision and rescheduling chances, definitely for ironic nodes, but also to some tiny extent for standard compute hosts as well. [0] http://logs.openstack.org/12/493812/2/check/gate-grenade-dsvm-ironic-multinode-multitenant-ubuntu-xenial/8d3f840/logs/old/screen-n-sch.txt.gz#_2017-08-15_13_27_29_410 [1] http://logs.openstack.org/12/493812/2/check/gate-grenade-dsvm- ironic-multinode-multitenant-ubuntu- xenial/8d3f840/logs/old/screen-n-sch.txt.gz#_2017-08-15_13_27_31_839 [2] http://logs.openstack.org/12/493812/2/check/gate-grenade-dsvm- ironic-multinode-multitenant-ubuntu- xenial/8d3f840/logs/old/screen-n-sch.txt.gz#_2017-08-15_13_27_34_244 [3] http://logs.openstack.org/12/493812/2/check/gate-grenade-dsvm- ironic-multinode-multitenant-ubuntu- xenial/8d3f840/logs/testr_results.html.gz To manage notifications about this bug go to: https://bugs.launchpad.net/nova/+bug/1711184/+subscriptions -- Mailing list: https://launchpad.net/~yahoo-eng-team Post to : yahoo-eng-team@lists.launchpad.net Unsubscribe : https://launchpad.net/~yahoo-eng-team More help : https://help.launchpad.net/ListHelp