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git2svn
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V 27
2021-03-15T03:04:25.809306Z
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V 962
Micro-optimize OOA queue processing.

- Move ctl_get_cmd_entry() calls from every OOA traversal to when
  the requests first inserted, storing seridx in struct ctl_scsiio.
- Move some checks out of the loop in ctl_check_ooa().
- Replace checks for errors that can not happen with asserts.
- Transpose ctl_serialize_table, so that any OOA traversal accessed
  only one row (cache line).  Compact it from enum to uint8_t.
- Optimize static branch predictions in hottest places.

Due to O(n) nature on deep LUN queues this can be the hottest code
path in CTL, and additional 20% of IOPS I see in some 4KB I/O tests
are good to have in reserve.  About 50% of CPU time here according
to the profiles is now spent in two memory accesses per traversed
request in OOA.

Sponsored by:	iXsystems, Inc.
MFC after:	2 weeks

(cherry picked from commit 9d9fd8b79f0ebe59f791c8225fa01ab59858b7b5)

Git Hash:   7b4859b4a26a1725f8e09bc6b8ae45007a8c43b4
Git Author: mav@FreeBSD.org
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