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    SubjectRe: [PATCH RFC tip/core/rcu] accelerate grace period if last non-dynticked CPU
    On Tue, Jan 26, 2010 at 06:55:16PM -0500, Mathieu Desnoyers wrote:
    > * Andi Kleen (andi@firstfloor.org) wrote:
    > > "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> writes:
    > >
    > > Kind of offtopic to the original patch, but I couldn't
    > > resist...
    > >
    > > > +config RCU_FAST_NO_HZ
    > > > + bool "Accelerate last non-dyntick-idle CPU's grace periods"
    > > > + depends on TREE_RCU && NO_HZ && SMP
    > >
    > > Having such a thing as a config option doesn't really make
    > > any sense to me. Who would want to recompile their kernel
    > > to enable/disable this? If anything it should be runtime, or better
    > > just unconditionally on.
    > >
    > > In general RCU could probably reduce its number of "weird"
    > > Kconfig options.
    > >
    > > While I think I have a better understanding of RCU than a lot
    > > of normal users I often have no clue what to set there when
    > > building a kernel.
    >
    > Maybe we could keep them under a CONFIG_DEBUG_RCU umbrella. Compiling
    > out parts of the rcu options can be useful for debugging purposes, but
    > I agree with you that end users should not be bothered with that much
    > options when some of them are "obviously" wanted.
    >
    > OTOH, I understand that Paul seems to want to introduce new RCU
    > features gradually, without hitting all kernel users with bugs in newer
    > features. That's a sane approach to keep things generally stable, but
    > maybe it is time to set some of the stabilized RCU options to default Y
    > and move their config to the debug menu.

    That is indeed a big part of the motivation. ;-)

    Thanx, Paul

    > Let's see what Paul has to say about this...
    >
    > Thanks,
    >
    > Mathieu
    >
    > >
    > > -Andi
    > >
    > > --
    > > ak@linux.intel.com -- Speaking for myself only.
    >
    > --
    > Mathieu Desnoyers
    > OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


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