Messages in this thread | | | Date | Mon, 17 Aug 2020 11:16:33 +0200 | From | peterz@infradea ... | Subject | Re: [RFC][PATCH 1/9] irq_work: Cleanup |
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On Mon, Aug 17, 2020 at 11:03:25AM +0200, peterz@infradead.org wrote: > On Thu, Jul 23, 2020 at 09:14:11AM -0700, Paul E. McKenney wrote: > > > --- a/kernel/rcu/tree.c > > > +++ b/kernel/rcu/tree.c > > > @@ -1287,8 +1287,6 @@ static int rcu_implicit_dynticks_qs(stru > > > if (IS_ENABLED(CONFIG_IRQ_WORK) && > > > !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq && > > > (rnp->ffmask & rdp->grpmask)) { > > > - init_irq_work(&rdp->rcu_iw, rcu_iw_handler); > > > > We are actually better off with the IRQ_WORK_INIT_HARD() here rather > > than unconditionally at boot. > > Ah, but there isn't an init_irq_work() variant that does the HARD thing.
Ah you meant doing:
rdp->rcu_iw = IRQ_WORK_INIT_HARD(rcu_iw_handler)
But then it is non-obvious how that doesn't trample state. I suppose that rcu_iw_pending thing ensures that... I'll think about it.
> > The reason for this is that we get here only if a single grace > > period extends beyond 10.5 seconds (mainline) or beyond 30 seconds > > (many distribution kernels). Which almost never happens. And yes, > > rcutree_prepare_cpu() is also invoked as each CPU that comes online, > > not that this is all that common outside of rcutorture and boot time. ;-) > > What do you mean 'also' ? Afaict this is CPU bringup only code (initial > and hotplug). We really don't care about code there. It's the slowest > possible path we have in the kernel. > > > > - atomic_set(&rdp->rcu_iw.flags, IRQ_WORK_HARD_IRQ); > > > rdp->rcu_iw_pending = true; > > > rdp->rcu_iw_gp_seq = rnp->gp_seq; > > > irq_work_queue_on(&rdp->rcu_iw, rdp->cpu); >
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