Re: Blogbench RAID benchmarks

[Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>]

:
:>    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.
:
:Sam

    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.

					-Matt
					Matthew Dillon 
					<dillon@backplane.com>