Re: FreeBSD random I/O performance issues

[Matthew Dillon]

    I've committed an 80% fix for the random seek / write
    performance issue.  The rest of the fix will come later
    when Kirk commits his shared-lock-buffer-cache idea.

    I've committed it into -current and will MFC it into
    -stable in a week if there aren't any problems.  I
    do not intend to MFC it into 3.x.

    This should solve most of the random-I/O latency issues
    with read-after-write on buffers.  Basically what
    had to be done was to continue to call the clustering
    code as before (so reallocblks still gets called), but 
    only issue write_behind I/O if the writes are
    generally sequential.  If the writes are random, even 
    big writes, we do not issue write-behind I/O.

                                    -Matt



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