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    SubjectRe: frequent lockups in 3.18rc4
    On Thu, Dec 18, 2014 at 10:58:59PM -0500, Dave Jones wrote:
    > > lock debugging and other overheads (does this still have
    > > DEBUG_PAGEALLOC?) you really are getting into a "real" softlockup
    > > because things are scaling so horribly badly.
    > >
    > > If you now disable spinlock debugging and lockdep, hopefully that page
    > > table lock now doesn't always get hung up on the lockdep locking, so
    > > it starts scaling much better, and maybe you'd not see this...
    >
    > I can give it a shot. Hopefully there's some further mitigation that
    > could be done to allow a workload like this to survive under a debug
    > build though, as we've caught *so many* bugs with this stuff in the past.

    Turns out also that this build didn't have PROVE_LOCKING enabled.
    CONFIG_LOCKDEP was, but that just bloats the structures a little, and
    afaik doesn't incur the same runtime overhead.

    I also forgot to answer the question above, PAGEALLOC is also off.

    So the only thing that was on that could cause spinlock overhead
    was DEBUG_SPINLOCK (and LOCK_STAT, though iirc that's not huge either)

    Dave


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