Re: [PATCH 2/2] rcu: Force resched_cpu when jiffies >= rcu_state.jiffies_resched
From: Paul E. McKenney
Date: Fri Nov 25 2016 - 03:37:59 EST
On Tue, Nov 22, 2016 at 05:12:20PM +0900, Byungchul Park wrote:
> On Wed, Nov 09, 2016 at 03:32:15PM +0900, Byungchul Park wrote:
> > Currently rcu code forces CPU into scheduler when jiffies >=
> > rcu_state.gp_start + jiffies_till_sched_qs, via resched_cpu().
> > It would be better to force CPU into scheduler when jiffies >=
> > rcu_state.jiffies_resched, too.
> I think these two patches are necessary to call resched_cpu() even in
> case of jiffies >= rcu_state.jiffies_resched, too. Am I wrong?
> It would be appriciated if you let me know if I was wrong.
My current thought is that both the "if" statement and the call to
resched_cpu() should be removed, but I am still testing and working
through the timing.
Either way, I do very much appreciate your having called my attention
to this code!
> Thank you,
> > Signed-off-by: Byungchul Park <byungchul.park@xxxxxxx>
> > ---
> > kernel/rcu/tree.c | 5 ++---
> > 1 file changed, 2 insertions(+), 3 deletions(-)
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index d8e8859..287f468 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -1217,11 +1217,10 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
> > READ_ONCE(*rcrmp) + rdp->rsp->flavor_mask);
> > }
> > rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */
> > - }
> > - /* And if it has been a really long time, kick the CPU as well. */
> > - if (ULONG_CMP_GE(jiffies, rdp->rsp->gp_start + jiffies_till_sched_qs))
> > + /* And if it has been a really long time, kick the CPU as well. */
> > resched_cpu(rdp->cpu); /* Force CPU into scheduler. */
> > + }
> > return 0;
> > }
> > --
> > 1.9.1