Messages in this thread Patch in this message | | | Date | Tue, 2 Jun 2015 05:36:13 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [GIT PULL rcu/next] RCU commits for 4.2 |
| |
On Tue, Jun 02, 2015 at 08:31:53AM +0200, Ingo Molnar wrote: > * Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote: > > > Hello, Ingo, > > > > The changes in this series include the following: > > > > 1. Remove all uses of RCU-protected array indexes. These were posted > > to LKML at https://lkml.org/lkml/2015/5/12/827. > > > > 2. Documentation updates. These were posted to LKML at > > https://lkml.org/lkml/2015/5/12/848. > > > > 3. Miscellaneous fixes. These were posted to LKML at > > https://lkml.org/lkml/2015/5/12/876. > > > > 4. CPU-hotplug updates. These were posted to LKML at > > https://lkml.org/lkml/2015/5/12/880. > > > > 5. Initialization/Kconfig updates. These were posted to LKML at > > https://lkml.org/lkml/2015/5/12/918, however, the updates to > > Tree RCU's initialization have been deferred to 4.3. > > > > 6. Updates to Tiny RCU. These were posted to LKML at > > https://lkml.org/lkml/2015/5/12/957. > > > > 7. Torture-testing updates. These were posted to LKML at > > https://lkml.org/lkml/2015/5/12/964.
[ . . . ]
> Pulled, thanks a lot Paul! > > I am wondering about the following small detail. You have reworked the whole RCU > Kconfig machinery with the introduction of RCU_EXPERT and smart selection of > defaults. (very nice!) > > There's a single interactive option left when a user configures RCU 'anew' and > keeps CONFIG_RCU_EXPERT disabled: > > Offload RCU callback processing from boot-selected CPUs (RCU_NOCB_CPU) [N/y/?] (NEW) > > I'm wondering whether we could put this behind CONFIG_RCU_EXPERT as well, and > disable it by default? > > The argument for this is very simple IMHO: NO_HZ_FULL depends on nocb_cpu support, > and actually selects it, so there's no way to misconfigure it. > > Without NO_HZ_FULL it might still make sense to use nocb_cpu, but it's very much > an advanced, expert option. > > With this change we could make RCU essentially configuration free in the common > case! :-)
And the -rt folks could presumably add a select clause as well, where needed. And I cannot recall a specific reason for not doing so. I have queued the following patch, so let's see how it goes. ;-)
Thanx, Paul
------------------------------------------------------------------------
rcu: Hide RCU_NOCB_CPU behind RCU_EXPERT This commit prevents Kconfig from asking the user about RCU_NOCB_CPU unless the user really wants to be asked. Reported-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Thomas Gleixner <tglx@linutronix.de>
diff --git a/init/Kconfig b/init/Kconfig index 5b8726c10685..67a0156fa091 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -697,6 +697,7 @@ config RCU_BOOST_DELAY config RCU_NOCB_CPU bool "Offload RCU callback processing from boot-selected CPUs" depends on TREE_RCU || PREEMPT_RCU + depends on RCU_EXPERT default n help Use this option to reduce OS jitter for aggressive HPC or
| |