On Mon, Aug 19, 2019 at 02:59:08PM +0200, Frederic Weisbecker wrote: > On Fri, Aug 16, 2019 at 09:52:42AM -0700, Paul E. McKenney wrote: > > On Fri, Aug 16, 2019 at 12:24:04PM -0400, Joel Fernandes wrote: > > > On Thu, Aug 15, 2019 at 10:53:11PM -0400, Joel Fernandes (Google) wrote: > > > > I really cannot explain this patch, but without it, the "else if" block > > > > just doesn't execute thus causing the tick's dep mask to not be set and > > > > causes the tick to be turned off. > > > > > > > > I tried various _ONCE() macros but the only thing that works is this > > > > patch. > > > > > > > > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > > > > --- > > > > kernel/rcu/tree.c | 3 ++- > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > > index 856d3c9f1955..ac6bcf7614d7 100644 > > > > --- a/kernel/rcu/tree.c > > > > +++ b/kernel/rcu/tree.c > > > > @@ -802,6 +802,7 @@ static __always_inline void rcu_nmi_enter_common(bool irq) > > > > { > > > > struct rcu_data *rdp = this_cpu_ptr(&rcu_data); > > > > long incby = 2; > > > > + int dnn = rdp->dynticks_nmi_nesting; > > > > > > I believe the accidental sign extension / conversion from long to int was > > > giving me an illusion since things started working well. Changing the 'int > > > dnn' to 'long dnn' gives similar behavior as without this patch! At least I > > > know now. Please feel free to ignore this particular RFC patch while I debug > > > this more (over the weekend or early next week). The first 2 patches are > > > good, just ignore this one. > > > > Ah, good point on the type! So you were ending up with zero due to the > > low-order 32 bits of DYNTICK_IRQ_NONIDLE being zero, correct? If so, > > the "!rdp->dynticks_nmi_nesting" instead needs to be something like > > "rdp->dynticks_nmi_nesting == DYNTICK_IRQ_NONIDLE", which sounds like > > it is actually worse then the earlier comparison against the constant 2. > > > > Sounds like I should revert the -rcu commit 805a16eaefc3 ("rcu: Force > > nohz_full tick on upon irq enter instead of exit"). > > I can't find that patch so all I can say so far is that its title doesn't > inspire me much. Do you still need that change for some reason? No we don't need it. Paul's dev branch fixed it by checking DYNTICK_IRQ_NONIDLE: https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?h=dev&id=227482fd4f3ede0502b586da28a59971dfbac0b0 thanks, - Joel