Re: We really ought to do something about O_DIRECT and data=journalled on ext4

All,

Geirth's results from his FreeBSD 7.1 server using 8.4's test_fsync:

Simple write timing:
        write                    0.007081

Compare fsync times on write() and non-write() descriptor:
If the times are similar, fsync() can sync data written
on a different descriptor.
        write, fsync, close      5.937933
        write, close, fsync      8.056394

Compare one o_sync write to two:
        one 16k o_sync write     7.366927
        two 8k o_sync writes    15.299300

Compare file sync methods with one 8k write:
        (o_dsync unavailable)
        open o_sync, write       7.512682
        (fdatasync unavailable)
        write, fsync             5.856480

Compare file sync methods with two 8k writes:
        (o_dsync unavailable)
        open o_sync, write      15.472910
        (fdatasync unavailable)
        write, fsync             5.880319


... again, open_sync does not look very impressive.

-- 
                                  -- Josh Berkus
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