Messages in this thread | | | Date | Tue, 18 Apr 2017 11:42:07 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH v2 tip/core/rcu 04/11] rcu: Make RCU_FANOUT_LEAF help text more explicit about skew_tick |
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On Mon, Apr 17, 2017 at 05:18:25PM -0700, Josh Triplett wrote: > 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.
Right you are! Fixed, thank you!
Thanx, Paul
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