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    SubjectRe: [PATCH v2 tip/core/rcu 04/11] rcu: Make RCU_FANOUT_LEAF help text more explicit about skew_tick
    On Mon, Apr 17, 2017 at 04:28:51PM -0700, Paul E. McKenney wrote:
    > If you set RCU_FANOUT_LEAF too high, you can get lock contention
    > on the leaf rcu_node, and you should boot with the skew_tick kernel
    > parameter set in order to avoid this lock contention. This commit
    > therefore upgrades the RCU_FANOUT_LEAF help text to explicitly state
    > this.
    >
    > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    > ---
    > init/Kconfig | 10 ++++++++--
    > 1 file changed, 8 insertions(+), 2 deletions(-)
    >
    > diff --git a/init/Kconfig b/init/Kconfig
    > index a92f27da4a27..946e561e67b7 100644
    > --- a/init/Kconfig
    > +++ b/init/Kconfig
    > @@ -612,11 +612,17 @@ config RCU_FANOUT_LEAF
    > initialization. These systems tend to run CPU-bound, and thus
    > are not helped by synchronized interrupts, and thus tend to
    > skew them, which reduces lock contention enough that large
    > - leaf-level fanouts work well.
    > + leaf-level fanouts work well. That said, setting leaf-level
    > + fanout to a large number will likely cause problematic
    > + lock contention on the leaf-level rcu_node structures unless
    > + you boot with the skew_tick kernel parameter.
    >
    > Select a specific number if testing RCU itself.
    >
    > - Select the maximum permissible value for large systems.
    > + Select the maximum permissible value for large systems, but
    > + please understand that you may also need to set the
    > + skew_tick kernel boot parameter to avoid contention
    > + on the rcu_node structure's locks.

    Nit: the indentation seems wrong here.

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