On Fri, Jul 06, 2012 at 09:31:29AM -0700, Paul E. McKenney wrote:
> On Fri, Jul 06, 2012 at 02:00:13PM +0200, Frederic Weisbecker wrote:
> > Create a new config option under the RCU menu that put
> > CPUs under RCU extended quiescent state (as in dynticks
> > idle mode) when they run in userspace. This require
> > some contribution from architectures to hook into kernel
> > and userspace boundaries.
> >
> > Signed-off-by: Frederic Weisbecker <fweis...@gmail.com>
> > Cc: Alessio Igor Bogani <abog...@kernel.org>
> > Cc: Andrew Morton <a...@linux-foundation.org>
> > Cc: Avi Kivity <a...@redhat.com>
> > Cc: Chris Metcalf <cmetc...@tilera.com>
> > Cc: Christoph Lameter <c...@linux.com>
> > Cc: Geoff Levand <ge...@infradead.org>
> > Cc: Gilad Ben Yossef <gi...@benyossef.com>
> > Cc: Hakan Akkan <hakanak...@gmail.com>
> > Cc: H. Peter Anvin <h...@zytor.com>
> > Cc: Ingo Molnar <mi...@kernel.org>
> > Cc: Josh Triplett <j...@joshtriplett.org>
> > Cc: Kevin Hilman <khil...@ti.com>
> > Cc: Max Krasnyansky <m...@qualcomm.com>
> > Cc: Peter Zijlstra <pet...@infradead.org>
> > Cc: Stephen Hemminger <shemmin...@vyatta.com>
> > Cc: Steven Rostedt <rost...@goodmis.org>
> > Cc: Sven-Thorsten Dietrich <thebigcorporat...@gmail.com>
> > Cc: Thomas Gleixner <t...@linutronix.de>
> > ---
> > arch/Kconfig | 13 +++++++++++++
> > init/Kconfig | 10 ++++++++++
> > kernel/rcutree.c | 4 ++++
> > 3 files changed, 27 insertions(+), 0 deletions(-)
> >
> > diff --git a/arch/Kconfig b/arch/Kconfig
> > index 8c3d957..c2e0ce4 100644
> > --- a/arch/Kconfig
> > +++ b/arch/Kconfig
> > @@ -274,4 +274,17 @@ config SECCOMP_FILTER
> >
> > See Documentation/prctl/seccomp_filter.txt for details.
> >
> > +config HAVE_RCU_USER_QS
> > + bool
> > + help
> > + Provide kernel entry/exit hooks necessary for userspace
> > + RCU extended quiescent state. Syscalls and exceptions
> > + low level handlers must be wrapped with a call to rcu_user_exit()
> > + on entry and rcu_user_enter() before resuming userspace. Irqs
> > + entry don't need to call rcu_user_exit() because their high level
> > + handlers are protected inside rcu_irq_enter/rcu_irq_exit() but
> > + preemption or signal handling on irq exit still need to be protected
> > + with a call to rcu_user_exit(). rcu_user_enter() must then be
> > + called back on irq exit when the preempted task is back on the CPU.
> > +
> > source "kernel/gcov/Kconfig"
> > diff --git a/init/Kconfig b/init/Kconfig
> > index d07dcf9..3a4af8f 100644
> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -441,6 +441,16 @@ config PREEMPT_RCU
> > This option enables preemptible-RCU code that is common between
> > the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.
> >
> > +config RCU_USER_QS
> > + bool "Consider userspace as in RCU extended quiescent state"
> > + depends on HAVE_RCU_USER_QS && SMP
>
> OK, I'll bite... Why the "SMP"? RCU could make good use of knowing
> about user-mode executing even in UP kernels.
Because Tiny RCU doesn't implement rcu_user_enter()/exit yet. And it
doesn't need it for now.
To better express the constraint I should probably have used:
depends on TREE_RCU || TREE_PREEMPT_RCU
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