Messages in this thread Patch in this message | | | Date | Wed, 28 Oct 2020 21:02:43 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFC][PATCH v3 6/6] rcu/tree: Use irq_work_queue_remote() |
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On Wed, Oct 28, 2020 at 03:54:28PM +0100, Peter Zijlstra wrote: > On Wed, Oct 28, 2020 at 12:07:13PM +0100, Peter Zijlstra wrote: > > AFAICT we only need/use irq_work_queue_on() on remote CPUs, since we > > can directly access local state. So avoid the IRQ_WORK dependency and > > use the unconditionally available irq_work_queue_remote(). > > > > This survives a number of TREE01 runs. > > OK, Paul mentioned on IRC that while it is extremely unlikely, this code > does not indeed guarantee it will not try to IPI self. > > I'll try again.
This is the best I could come up with.. :/
--- Subject: rcu/tree: Use irq_work_queue_remote() From: Peter Zijlstra <peterz@infradead.org> Date: Wed Oct 28 11:53:40 CET 2020
All sites that consume rcu_iw_gp_seq seem to have rcu_node lock held, so setting it probably should too. Also the effect of self-IPI here would be setting rcu_iw_gp_seq to the value we just set it to (pointless) and clearing rcu_iw_pending, which we just set, so don't set it.
Passes TREE01.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- kernel/rcu/tree.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
--- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1308,14 +1308,16 @@ static int rcu_implicit_dynticks_qs(stru resched_cpu(rdp->cpu); WRITE_ONCE(rdp->last_fqs_resched, jiffies); } -#ifdef CONFIG_IRQ_WORK + raw_spin_lock_rcu_node(rnp); if (!rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq && (rnp->ffmask & rdp->grpmask)) { - rdp->rcu_iw_pending = true; rdp->rcu_iw_gp_seq = rnp->gp_seq; - irq_work_queue_on(&rdp->rcu_iw, rdp->cpu); + if (likely(rdp->cpu != smp_processor_id())) { + rdp->rcu_iw_pending = true; + irq_work_queue_remote(rdp->cpu, &rdp->rcu_iw); + } } -#endif + raw_spin_unlock_rcu_node(rnp); } return 0;
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