DO NOT MERGE: nvme_driver: delay io queue create to be post restore iff there are no ouststanding IO to that queue (#2456) #2495
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…o ouststanding IO to that queue (microsoft#2456) Looking at production data, I found that restoring the IO queues took significantly longer than I expected. In those same runs, there was no outstanding IO to those queues at the time of save. Since there's no outstanding IO, there's no need to create the IO queue at restore time: the purpose of creating the queue would be to handle completions. No pending commands means no completions. This won't help in the case where every IO QP has outstanding commands, but it will help in cases where there are idle devices. And, philosophically, we want to do as little during VP blackout as we can get away with.
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Creating now to make sure we don't forget about this PR. But, I'd like to get additional test coverage in main before I complete. Will check back the 1st week of December. |
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Clean cherry pick of PR #2456.
Looking at production data, I found that restoring the IO queues took
significantly longer than I expected. In those same runs, there was no
outstanding IO to those queues at the time of save. Since there's no
outstanding IO, there's no need to create the IO queue at restore time:
the purpose of creating the queue would be to handle completions. No
pending commands means no completions.
This won't help in the case where every IO QP has outstanding commands,
but it will help in cases where there are idle devices. And,
philosophically, we want to do as little during VP blackout as we can
get away with.