lkml.org 
[lkml]   [2013]   [Jan]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH tip/core/rcu 04/14] rcu: Provide compile-time control for no-CBs CPUs
On Sat, Jan 05, 2013 at 09:48:54AM -0800, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paul.mckenney@linaro.org>
>
> Currently, the only way to specify no-CBs CPUs is via the rcu_nocbs
> kernel command-line parameter. This is inconvenient in some cases,
> particularly for randconfig testing, so this commit adds a new
> RCU_NOCB_CPU_DEFAULT kernel configuration parameter. Setting this
> new parameter to zero (the default) retains the old behavior, setting
> it to one offloads callback processing from CPU 0 (along with any
> other CPUs specified by the rcu_nocbs boot-time parameter), and setting
> it to two offloads callback processing from all CPUs.
>
> Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Comments below.

> init/Kconfig | 13 +++++++++++++
> kernel/rcutree_plugin.h | 13 +++++++++++++
> 2 files changed, 26 insertions(+), 0 deletions(-)
>
> diff --git a/init/Kconfig b/init/Kconfig
> index fc6a3ca..35dcedb 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -676,6 +676,19 @@ config RCU_NOCB_CPU
> Say Y here if you want to help to debug reduced OS jitter.
> Say N here if you are unsure.
>
> +config RCU_NOCB_CPU_DEFAULT
> + int "Offload RCU callback processing from compile-selected CPUs"
> + depends on RCU_NOCB_CPU
> + range 0 2
> + default 0
> + help
> + Set this option to zero to only offload RCU callback processing
> + from those CPUs specified by the boot-time rcu_nocbs kernel
> + parameter. Set it to one to offload processing from CPU 0
> + in addition to any CPUs specified at boot time. Set it to
> + two to offload processing from all CPUs, regardless of the
> + setting of the boot-time rcu_nocbs kernel parameter.
> +

Rather than making users translate the meanings of 0, 1, and 2, this
seems like something better done with a choice/endchoice; that would
then offer a menu of options that can each have their own description.
Take a look at the "Memory split" option in arch/x86/Kconfig for an
example.

> --- a/kernel/rcutree_plugin.h
> +++ b/kernel/rcutree_plugin.h
> @@ -86,6 +86,19 @@ static void __init rcu_bootup_announce_oddness(void)
> if (nr_cpu_ids != NR_CPUS)
> printk(KERN_INFO "\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
> #ifdef CONFIG_RCU_NOCB_CPU
> +#if CONFIG_RCU_NOCB_CPU_DEFAULT != 0

That would then make each of these conditionals self-documenting as
well.

- Josh Triplett


\
 
 \ /
  Last update: 2013-01-07 19:21    [W:0.084 / U:0.556 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site