linux-kernel - [RFC][PATCH v3 6/6] rcu/tree: Use irq_work_queue

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Date:   Wed, 28 Oct 2020 12:07:13 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org
Cc:     linux-kernel@...r.kernel.org, will@...nel.org, paulmck@...nel.org,
        hch@....de, axboe@...nel.dk, chris@...is-wilson.co.uk,
        davem@...emloft.net, kuba@...nel.org, fweisbec@...il.com,
        oleg@...hat.com, vincent.guittot@...aro.org, peterz@...radead.org
Subject: [RFC][PATCH v3 6/6] rcu/tree: Use irq_work_queue_remote()

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.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/rcu/tree.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1308,14 +1308,12 @@ static int rcu_implicit_dynticks_qs(stru
 			resched_cpu(rdp->cpu);
 			WRITE_ONCE(rdp->last_fqs_resched, jiffies);
 		}
-#ifdef CONFIG_IRQ_WORK
 		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);
+			irq_work_queue_remote(rdp->cpu, &rdp->rcu_iw);
 		}
-#endif
 	}
 
 	return 0;