On Mon, Mar 07, 2022 at 12:17:55PM +0100, Sebastian Andrzej Siewior wrote:
> On 2022-03-04 20:40:07 [-0800], Paul E. McKenney wrote:
> > > This is what I had in mind. Does this work for you?
> >
> > This does seem to be working, thank you! I even manually inserted
> > a pi_lock() acquisition across one of the calls to call_rcu_tasks(),
> > and it did seem to work.
>
> perfect.
Sounds like I should add that to rcutorture.
> > > kernel/rcu/tasks.h | 14 ++++++++------
> > > 1 file changed, 8 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> > > index d64f0b1d8cd3b..f804afb304135 100644
> > > --- a/kernel/rcu/tasks.h
> > > +++ b/kernel/rcu/tasks.h
> > > @@ -113,11 +113,11 @@ static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp);
> > > #define DEFINE_RCU_TASKS(rt_name, gp, call, n) \
> > > static DEFINE_PER_CPU(struct rcu_tasks_percpu, rt_name ## __percpu) = { \
> > > .lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name ## __percpu.cbs_pcpu_lock), \
> > > - .rtp_irq_work = IRQ_WORK_INIT(call_rcu_tasks_iw_wakeup), \
> > > + .rtp_irq_work = IRQ_WORK_INIT_HARD(call_rcu_tasks_iw_wakeup), \
> >
> > This is the key piece, right?
>
> Correct. Possible due to the removal of wait_queue_head (plus there is
> nothing else that would stand in the way otherwise).
Very good!
If the overhead becomes a problem in mainline, presumably we can do
a compile-time switch based on CONFIG_PREEMPT_RT or similar.
> > If so, I am wondering if there are other
> > irq_work instances that need to move to _HARD.
>
> We already have:
> kernel/rcu/tree.c: rdp->rcu_iw = IRQ_WORK_INIT_HARD(rcu_iw_handler);
Because you prompted me to change it from IRQ_WORK_INIT() some time
back? ;-)
Thanx, Paul
