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5.x filesystem performance regression

Having fixed my performace-critical RAID configuration, I think there's some
serious filesystem performance regression from 4.x to 5.x.

I've tested every possible combination of 4.0.1 vs. 5.1, softdep vs. WAPBL,
parity maps enabled vs. disabled, bare disc vs. RAID 1 vs. RAID 5.
The test case was extracting the 5.1 src.tgz set onto the filesystem under test.
The extraction was done twice (having deleted the extracted tree in between);
in some cases the time for the first run is missing because I forgot to time
the tar command.
All tests are on identical hardware, a 4G amd64 system with three Seagate
ST336607LW discs on an Adaptec 19160 SCSI controller.

In the following table, the two figures in each column are elapsed seconds
for the two runs.

                plain disc      RAID 1          RAID 5 16k      RAID 5 32k
4.0.1 softdep   64s     12s     ?       11s     ?       17s     54s     12s
5.1 softdep     51s     42s     65s     60s     330s    347s    218s    250s
5.1 log         66s     30s     84s     25s     ?       426s    194s    190s
5.1 softdep, no parity map      63s     61s     339s    331s    not measured
5.1 log, no parity map          88s     26s     ?       340s    not measured

Both RAIDs have 32 sectPerSU.
The filesystem on the RAID 1 has a 16k bsize, on RAID 5, I tested both 16k/32k.

So, almost everywhere, 4.0.1 is three to fiveteen times as fast as 5.1.

Any ideas where to look further? Anyone to confirm my measurements?

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