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DragonFly kernel List (threaded) for 2011-07
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Re: Blogbench RAID benchmarks

From: Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>
Date: Mon, 11 Jul 2011 16:34:50 -0700 (PDT)

:>    I'm not sure where the concurrency is breaking down on the RAID subsystem,
:>    it could be due to that particular driver still being under the big
:>    giant lock (the AHCI and SILI drivers don't use the bgl, but arcmsr
:>    driver probably still does).
:arcmsr uses lockmgr and is not under the mplock at all. Which is not
:to say it isn't still serializing internally somewhere, but it should
:not be any different than FreeBSD in this regard.

    Hmm.  There are two major locking points for a (CAM based) disk driver.
    The first is the lock passed in cam_sim_alloc().  The second is whether
    INTR_MPSAFE is passed to bus_setup_intr().

    It looks like arcmsr is passing its own lock to cam_sim_alloc(), but
    is *not* passing the INTR_MPSAFE flag to bus_setup_intr().

    I haven't reviewed the interrupt handling code to determine how safe
    the functions it calls internally are.  arcmsr does get its own lock
    in arcmsr_intr_handler().  It could very well be safe for us to set
    the INTR_MPSAFE flag there but someone will have to life-test it.

    In anycase, I'm not sure it's even the bottleneck for the earlier tests
    since blockbench didn't run long enough (with default options) to use
    up 32G of ram.

					Matthew Dillon 

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