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From: "Paul E. McKenney" <paulmck@linux.ibm.com>
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org,
	jiangshanlai@gmail.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
	rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
	fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
	"Paul E. McKenney" <paulmck@linux.ibm.com>
Subject: [PATCH RFC v2 tip/core/rcu 4/4] rcu: Allow rcu_read_unlock_special() to raise_softirq() if in_irq()
Date: Tue,  2 Apr 2019 07:38:42 -0700	[thread overview]
Message-ID: <20190402143842.16068-4-paulmck@linux.ibm.com> (raw)
In-Reply-To: <20190402143758.GA15134@linux.ibm.com>

When running in an interrupt handler, raise_softirq() and
raise_softirq_irqoff() have extremely low overhead: They simply set a
bit in a per-CPU mask, which is checked upon exit from that interrupt
handler.  Therefore, if rcu_read_unlock_special() is invoked within an
interrupt handler and RCU_SOFTIRQ is in use, this commit make use of
raise_softirq_irqoff() even if there is no expedited grace period in
flight and even if this is not a nohz_full CPU.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
---
 kernel/rcu/tree_plugin.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index d15cdab6aeb4..e1005f5e8094 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -615,7 +615,7 @@ static void rcu_read_unlock_special(struct task_struct *t)
 		      (rdp->grpmask & rnp->expmask) ||
 		      tick_nohz_full_cpu(rdp->cpu);
 		// Need to defer quiescent state until everything is enabled.
-		if (exp && irqs_were_disabled && use_softirq &&
+		if ((exp || in_irq()) && irqs_were_disabled && use_softirq &&
 		    (in_irq() || !t->rcu_read_unlock_special.b.deferred_qs)) {
 			// Using softirq, safe to awaken, and we get
 			// no help from enabling irqs, unlike bh/preempt.
-- 
2.17.1


      parent reply	other threads:[~2019-04-02 14:38 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-02 14:37 [PATCH RFC v2 tip/core/rcu 0/4] Real-time elimination of RCU_SOFTIRQ Paul E. McKenney
2019-04-02 14:38 ` [PATCH RFC v2 tip/core/rcu 1/4] rcu: Enable elimination of Tree-RCU softirq processing Paul E. McKenney
2019-04-02 14:38 ` [PATCH RFC v2 tip/core/rcu 2/4] rcu: Check for wakeup-safe conditions in rcu_read_unlock_special() Paul E. McKenney
2019-04-02 14:38 ` [PATCH RFC v2 tip/core/rcu 3/4] rcu: Only do rcu_read_unlock_special() wakeups if expedited Paul E. McKenney
2019-04-02 14:38 ` Paul E. McKenney [this message]

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