On Fri, Jul 11, 2014 at 03:47:37PM +0200, Frederic Weisbecker wrote:
> On Fri, Jul 11, 2014 at 06:35:03AM -0700, Paul E. McKenney wrote:
> > From: "Paul E. McKenney" <paul...@linux.vnet.ibm.com>
> >
> > Enabling NO_HZ_FULL currently has the side effect of enabling callback
> > offloading on all CPUs. This results in lots of additional rcuo kthreads,
> > and can also increase context switching and wakeups, even in cases where
> > callback offloading is neither needed nor particularly desirable. This
> > commit therefore enables callback offloading on a given CPU only if
> > specifically requested at build time or boot time, or if that CPU has
> > been specifically designated (again, either at build time or boot time)
> > as a nohz_full CPU.
> >
> > Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
>
> ACK.
I thought you might like this one. ;-)
Thanx, Paul
> > ---
> > init/Kconfig | 4 ++--
> > kernel/rcu/tree_plugin.h | 3 +++
> > 2 files changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/init/Kconfig b/init/Kconfig
> > index 9d76b99af1b9..9332d33346ac 100644
> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -737,7 +737,7 @@ choice
> >
> > config RCU_NOCB_CPU_NONE
> > bool "No build_forced no-CBs CPUs"
> > - depends on RCU_NOCB_CPU && !NO_HZ_FULL
> > + depends on RCU_NOCB_CPU && !NO_HZ_FULL_ALL
> > help
> > This option does not force any of the CPUs to be no-CBs CPUs.
> > Only CPUs designated by the rcu_nocbs= boot parameter will be
> > @@ -751,7 +751,7 @@ config RCU_NOCB_CPU_NONE
> >
> > config RCU_NOCB_CPU_ZERO
> > bool "CPU 0 is a build_forced no-CBs CPU"
> > - depends on RCU_NOCB_CPU && !NO_HZ_FULL
> > + depends on RCU_NOCB_CPU && !NO_HZ_FULL_ALL
> > help
> > This option forces CPU 0 to be a no-CBs CPU, so that its RCU
> > callbacks are invoked by a per-CPU kthread whose name begins
> > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> > index b27b86c7bbfa..17eed0856b03 100644
> > --- a/kernel/rcu/tree_plugin.h
> > +++ b/kernel/rcu/tree_plugin.h
> > @@ -2473,6 +2473,9 @@ static void __init rcu_spawn_nocb_kthreads(struct
> > rcu_state *rsp)
> >
> > if (rcu_nocb_mask == NULL)
> > return;
> > +#ifdef CONFIG_NO_HZ_FULL
> > + cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
> > +#endif /* #ifdef CONFIG_NO_HZ_FULL */
> > if (ls == -1) {
> > ls = int_sqrt(nr_cpu_ids);
> > rcu_nocb_leader_stride = ls;
> > --
> > 1.8.1.5
> >
>
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