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    SubjectRe: [RFC patch 2/5] smpboot: Provide infrastructure for percpu hotplug threads
    On Thu, Jun 14, 2012 at 03:32:19PM +0200, Thomas Gleixner wrote:
    > On Thu, 14 Jun 2012, Paul E. McKenney wrote:
    > > On Thu, Jun 14, 2012 at 01:20:39PM +0200, Thomas Gleixner wrote:
    > > > I gave it a quick shot, but I was not able to reproduce the hang yet.
    > >
    > > Really? I have a strictly Western-Hemisphere bug? ;-)
    >
    > I guess I need to fire up rcu torture to make it surface.

    A simple offline was triggering it for me. Perhaps some of my debug
    code was inappropriate, will retry.

    > > > But looking at the thread function made me look into rcu_yield() and I
    > > > really wonder what kind of drug induced that particular piece of
    > > > horror.
    > >
    > > When you are working on something like RCU priority boosting, no other
    > > drug is in any way necessary. ;-)
    >
    > And how do we protect minors from that ?

    We rely on their own sense of self-preservation preventing them from
    getting involved in such insanity.

    > > > I can't figure out why this yield business is necessary at all. The
    > > > commit logs are as helpful as the missing code comments :)
    > > >
    > > > I suspect that it's some starvation issue. But if we need it, then
    > > > can't we replace it with something sane like the (untested) patch
    > > > below?
    > >
    > > Yep, starvation. I will take a look at your approach after I wake
    > > up a bit more.
    >
    > Btw, if that simpler yield approach is working and I can't see why it
    > shouldn't then you can get rid of the node task as well. The only
    > purpose of it is to push up the priority of yielding tasks, right?

    It also boosts the priority of preempted RCU read-side critical sections.

    Thanx, Paul



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