When some plugin was registered as "unschedulable" in some previous scheduling
attempt, it kept that attribute for a pod forever. When that plugin then later
failed with an error that requires backoff, the pod was incorrectly moved to the
"unschedulable" queue where it got stuck until the periodic flushing because
there was no event that the plugin was waiting for.
Here's an example where that happened:
framework.go:1280: E0831 20:03:47.184243] Reserve/DynamicResources: Plugin failed err="Operation cannot be fulfilled on podschedulingcontexts.resource.k8s.io \"test-dragxd5c\": the object has been modified; please apply your changes to the latest version and try again" node="scheduler-perf-dra-7l2v2" plugin="DynamicResources" pod="test/test-dragxd5c"
schedule_one.go:1001: E0831 20:03:47.184345] Error scheduling pod; retrying err="running Reserve plugin \"DynamicResources\": Operation cannot be fulfilled on podschedulingcontexts.resource.k8s.io \"test-dragxd5c\": the object has been modified; please apply your changes to the latest version and try again" pod="test/test-dragxd5c"
...
scheduling_queue.go:745: I0831 20:03:47.198968] Pod moved to an internal scheduling queue pod="test/test-dragxd5c" event="ScheduleAttemptFailure" queue="Unschedulable" schedulingCycle=9576 hint="QueueSkip"
Pop still needs the information about unschedulable plugins to update the
UnschedulableReason metric. It can reset that information before returning the
PodInfo for the next scheduling attempt.
The previous approach was based on the assumption that an in-flight pod can use
the head of the received event list as marker for identifying all events that
occur while the pod is in flight. That assumption is incorrect: when that
existing element gets removed from the list because all pods that were
in-flight when it was received are done, that marker's Next method returns nil
and the code which should have seen several concurrent events (if there were
any) missed all of those.
As a result, a pod with concurrent events could incorrectly get moved to the
unschedulable queue where it could got stuck until the next periodic purging
after 5 minutes if there was no other event for it.
The approach with maintaining a single list of concurrent events can be fixed
by inserting each in-flight pod into the list and using that element to
identify "more recent" events for the pod.
* feature(sscheduling_queue): track events per Pods
* fix typos
* record events in one slice and make each in-flight Pod to refer it
* fix: use Pop() in test before AddUnschedulableIfNotPresent to register in-flight Pods
* eliminate MakeNextPodFuncs
* call Done inside the scheduling queue
* fix comment
* implement done() not to require lock in it
* fix UTs
* improve the receivedEvents implementation based on suggestions
* call DonePod when we don't call AddUnschedulableIfNotPresent
* fix UT
* use queuehint to filter out events for in-flight Pods
* fix based on suggestion from aldo
* fix based on suggestion from Wei
* rename lastEventBefore → previousEvent
* fix based on suggestion
* address comments from aldo
* fix based on the suggestion from Abdullah
* gate in-flight Pods logic by the SchedulingQueueHints feature gate
