Improvements in HAMMER parallel I/O performance

[Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>]

    With the latest master people should be seeing some serious improvement
    in HAMMER's parallel I/O performance.  e.g. simultanious reads and
    writes, benchmarks, and so forth.  The improvements will be more
    pronounced if you are running SCSI, SILI, or the AHCI driver, but
    NATA will see a good chunk of the improvements too.

    These improvements are not in random I/O... e.g. find . or ls -lR on an
    uncached directory tree.  They are specifically for parallel I/O loads,
    aka blogbench and friends.

    I did some major work controlling buffer cache locking as it relates
    to HAMMER, to reduce lock contention, and some major work on
    bioqdisksort() to add write bleedover and write bursting to the
    read priority scheme.

					-Matt
					Matthew Dillon 
					<dillon@backplane.com>