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    SubjectRe: CONFIG_PREEMPT_RCU in next/mmotm
    On Sun, Aug 09, 2009 at 04:32:28AM +0100, Hugh Dickins wrote:
    > On Sat, 8 Aug 2009, Paul E. McKenney wrote:
    > > On Sat, Aug 08, 2009 at 08:34:03PM +0100, Hugh Dickins wrote:
    > >
    > > > CONFIG_PREEMPT_TREE=y seems okay on PowerPC; and when I briefly tried
    > >
    > > CONFIG_TREE_RCU=y, you mean, right?
    >
    > Whoops, yes indeed.
    >
    > > > My guess is that there's some other issue which is triggering
    > > > the RCU disgrace, but that is just a guess.
    > >
    > > The one other issue I know of is one that apparently happens only on
    > > one of Ingo's machines, which suddenly decides that it need not inform
    > > RCU when onlining a CPU (at boot time).
    > >
    > > But you seem to be making it past boot, and I would guess that you are
    > > not doing any hotplug CPU operations, right?
    >
    > That's right, I'm well past boot, and don't explicitly get into CPU
    > hotplug, nor using suspend/hibernate on that machine; and looking at
    > the config, see I don't even have CONFIG_HOTPLUG_CPU set.
    >
    > In the morning I'll check that /proc/cpuinfo really shows all four
    > cpus before I start, and is still showing four cpus when it goes bad,
    > in case there's nevertheless an issue with that.
    >
    > Is there some particular attribute of a cpu, most relevant to its RCU
    > grace status, that I can check on with a printk?

    The debugfs files enabled by CONFIG_RCU_TRACE, except rcu/rcugp, which,
    since it will attempt to wait for a grace period, will probably wait
    forever.

    > > > Config attached. Any suggestions?
    >
    > [ Of course I forgot the config, but sent it just to Paul later. ]
    >
    > >
    > > /me scratches head... Will try some more CONFIG_PREEMPT_RCU testing
    > > locally.
    >
    > Thanks: I'm kind of glad that it's interesting,
    > though it may sink some of our time.

    Well, it certainly does have me a bit confused at the moment!

    Thanx, Paul


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