Update on recent SMP contention work (2)

[Matthew Dillon]

    Another veritible ton of SMP performance work has gone into master.

    * The entire [v]fork/exec/exit/wait path has been streamlined and
      essentially no longer have any SMP contention.

    * The pid/process-group/session mechanics have been rewritten and
      essentially no longer have any SMP contention.

    * The entire VM fault path, particularly for initial COWs on binaries
      (to support concurrent exec's) is now able to use shared fine-grained
      locks end-to-end and have no SMP contention.

      As in zero.  Running 8 threads doing fork/exec/wait of an ELF binary
      on one of the Haswell blades went from 10.60 seconds for 80000 total
      execs to 3.8 seconds.  That's a multi-fold 2.7x improvement in
      performance.

    * tmpfs performance has been radically improved.  It turns out that
      most of the code was fine-grained locked but still had coarse-grained
      per-mount locks wrapped around most of the VNOP operations.  I took
      pass on it and removed most of the coarse-grained locks.

    The previous block of work got rid of 90% of the contention on the
    smaller systems (the 4-core/8-thread blades), but were lacking on the
    bigger system (monster's 48-core opteron).

    This most recent set of work has gotten rid of 98% of the contention
    on the smaller systems and probably 90%+ of the contention on monster.

    The only system paths which still have noticable contention are the
    filesystem write paths.

    --

    Bulk package builds (dports) on monster are under test now, no results
    yet but the last week or two has brought the full build for 20,000+
    packages, from scratch, down to around 15-hours.   The current tests
    should be able to beat that.

    As with prior work, there may be some instability.  I will continue to
    work through what bugs show up and exercise various subsystems such as
    swapcache and paging under heavy loads to locate and fix whatever
    problems show up.

					-Matt
					Matthew Dillon 
					<dillon at backplane.com>