| Message ID | 1357408144-15830-4-git-send-email-paulmck@linux.vnet.ibm.com |
|---|---|
| State | New |
| Headers | show |
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
On Mon, Jan 07, 2013 at 08:50:23AM -0800, Josh Triplett wrote: > 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. My first reaction was that this couldn't possibly handle the dependency on CONFIG_RCU_NOCB_CPU, but it actually does work, suppressing all the choices when CONFIG_RCU_NOCB_CPU=n. Cute! > > --- 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. Indeed, much better! Thank you! Thanx, Paul
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. + endmenu # "RCU Subsystem" config IKCONFIG diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 37750bc..eb9b473 100644 --- 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 + if (!have_rcu_nocb_mask) { + alloc_bootmem_cpumask_var(&rcu_nocb_mask); + have_rcu_nocb_mask = true; + } +#if CONFIG_RCU_NOCB_CPU_DEFAULT == 1 + pr_info("\tExperimental no-CBs CPU 0\n"); + cpumask_set_cpu(0, rcu_nocb_mask); +#else /* #if CONFIG_RCU_NOCB_CPU_DEFAULT == 1 */ + pr_info("\tExperimental no-CBs for all CPUs\n"); + cpumask_setall(rcu_nocb_mask); +#endif /* #else #if CONFIG_RCU_NOCB_CPU_DEFAULT == 1 */ +#endif /* #if CONFIG_RCU_NOCB_CPU_DEFAULT != 0 */ if (have_rcu_nocb_mask) { cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask); pr_info("\tExperimental no-CBs CPUs: %s.\n", nocb_buf);