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.

> ---
>  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
> 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Reply via email to