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    SubjectRe: RCU qsmask !=0 warnings on large-SMP...
    On 1/25/2012 22:51, Paul E. McKenney wrote:
    > On Wed, Jan 25, 2012 at 09:35:15PM +0100, Steffen Persvold wrote:
    []
    >>
    >> Yes, 3.2.1 is our debug target right now.
    >
    > OK, good! Could you please add an "ftrace_dump(DUMP_ALL)" before you
    > print the first set of error messages? (Preferably set up so that
    > you only dump once!)
    >
    > Then before you start testing, could you please enable the
    > rcu_grace_period and rcu_grace_period_init trace events? This should
    > get a good picture of the sequence of grace-period-related events leading
    > up to the failure.
    >
    > You will need to build the kernel with CONFIG_RCU_TRACE=y.
    >
    > The usual commands suffice to enable tracing:
    >
    > echo 1> /sys/kernel/debug/tracing/events/rcu_grace_period/enable
    > echo 1> /sys/kernel/debug/tracing/events/rcu_grace_period_init/enable
    >
    > This should give some history that might help understand why the previous
    > grace period ended before the CPUs had all checked in. Maybe even why
    > the rcu_node structures got advance notice of the new grace period...
    >

    []

    >>
    >> Are you talking about the data from /sys/kernel/debug/rcu/ ? I have
    >> CONFIG_RCU_TRACE (and consequently CONFIG_TREE_RCU_TRACE) set, is
    >> this enough to get the event data you want ?
    >
    > Yep, if you have CONFIG_RCU_TRACE=y, then the two tracepoints should
    > be available.
    >

    It seems that I don't have the /sys/kernel/debug/tracing/events
    interface on the kernel I'm running now. Perhaps I need to enable the
    CONFIG_FTRACE feature also ? If so what FTRACE interfaces do I need ?

    Cheers,
    --
    Steffen Persvold, Chief Architect NumaChip
    Numascale AS - www.numascale.com
    Tel: +47 92 49 25 54 Skype: spersvold


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