bmarcott edited a comment on issue #26696: [WIP][SPARK-18886][CORE] Only reset 
scheduling delay timer if allocated slots are fully utilized
URL: https://github.com/apache/spark/pull/26696#issuecomment-561438844
 
 
   What were the particular critiques of this PR?
   
   I suggest reading, particularly Kay's comments, 
[SPARK-18886](https://issues.apache.org/jira/browse/SPARK-18886?jql=project%20%3D%20SPARK%20AND%20text%20~%20delay)
 as well as the comments [in this old 
PR](https://github.com/apache/spark/pull/9433).
   
   Below ideas I have seen (and some I tried) have the following issues:
   1. Never reset timer: delay scheduling only works on first wave (as 
@tgravescs  pointed out)
   2. Per slot timer: delay scheduling should apply per task/taskset (as I 
pointed out above) which might lead you to # 3
   3. Per slot per stage timer: tasks can be starved by being offered many 
different slots, each starting a new timer). also too much bookkeeping
   4. Per task timer: you still need a way to distinguish between when a task 
is waiting for a slot to become available vs it has them available but is not 
utilizing them (which is what this PR does). To do this right seems to be this 
PR + more timers.
   
   

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