On Fri, Apr 29, 2011 at 01:36:18AM -0700, Paul E. McKenney wrote:
> On Thu, Apr 28, 2011 at 12:52:02PM +0300, Gleb Natapov wrote:
>
> Hmmm.... This is interesting. KVM being a module, we either expand
> TINY_RCU's size a bit by making rcu_note_context_switch() be a real
> function in rcutiny.c and adding an export, or we expand it by adding
> two exports.
>
> I would like to solve this without making TINY_RCU larger, and preferably
> by making it smaller. Any ideas come to mind? (Other than making
> KVM depend on CONFIG_SMP, which sounds too much like throwing out the
> baby with the bathwater.)
Nothing quite like hitting "send" to make an idea show up...
In a UP kernel, does it actually help anything to have KVM
tell RCU about executing in a guest? If not, could we have a
rcu_note_context_switch_kvm() that is a static inline empty function in
TINY_RCU and maps to rcu_note_context_switch() for TREE_RCU?
Thanx, Paul
> > Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx>
> > ---
> > include/linux/rcutiny.h | 6 +-----
> > kernel/rcutiny.c | 7 +++++++
> > kernel/rcutree.c | 1 +
> > 3 files changed, 9 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
> > index 30ebd7c..8e5f7cf 100644
> > --- a/include/linux/rcutiny.h
> > +++ b/include/linux/rcutiny.h
> > @@ -93,11 +93,7 @@ static inline int rcu_needs_cpu(int cpu)
> >
> > #endif /* #else #ifdef CONFIG_TINY_RCU */
> >
> > -static inline void rcu_note_context_switch(int cpu)
> > -{
> > - rcu_sched_qs(cpu);
> > - rcu_preempt_note_context_switch();
> > -}
> > +extern void rcu_note_context_switch(int cpu);
> >
> > /*
> > * Return the number of grace periods.
> > diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
> > index 0c343b9..3d715a4 100644
> > --- a/kernel/rcutiny.c
> > +++ b/kernel/rcutiny.c
> > @@ -78,6 +78,13 @@ void rcu_exit_nohz(void)
> >
> > #endif /* #ifdef CONFIG_NO_HZ */
> >
> > +void rcu_note_context_switch(int cpu)
> > +{
> > + rcu_sched_qs(cpu);
> > + rcu_preempt_note_context_switch();
> > +}
> > +EXPORT_SYMBOL_GPL(rcu_note_context_switch);
> > +
> > /*
> > * Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc().
> > * Also disable irqs to avoid confusion due to interrupt handlers
> > diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> > index dd4aea8..0837d63 100644
> > --- a/kernel/rcutree.c
> > +++ b/kernel/rcutree.c
> > @@ -124,6 +124,7 @@ void rcu_note_context_switch(int cpu)
> > rcu_sched_qs(cpu);
> > rcu_preempt_note_context_switch(cpu);
> > }
> > +EXPORT_SYMBOL_GPL(rcu_note_context_switch);
> >
> > #ifdef CONFIG_NO_HZ
> > DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
> > --
> > 1.7.2.3
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majordomo@xxxxxxxxxxxxxxx
> > More majordomo info at http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at http://www.tux.org/lkml/
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
