linux-kernel - [patch V2 7/9] softirq: Replace barrier() with cpu_relax() in tasklet_unlock

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Message-Id: <20201204170805.430113367@linutronix.de>
Date:   Fri, 04 Dec 2020 18:01:58 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paul McKenney <paulmck@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [patch V2 7/9] softirq: Replace barrier() with cpu_relax() in
 tasklet_unlock_wait()

From: Thomas Gleixner <tglx@...utronix.de>

A barrier() in a tight loop which waits for something to happen on a remote
CPU is a pointless exercise. Replace it with cpu_relax() which allows HT
siblings to make progress.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 include/linux/interrupt.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -668,7 +668,8 @@ static inline void tasklet_unlock(struct
 
 static inline void tasklet_unlock_wait(struct tasklet_struct *t)
 {
-	while (test_bit(TASKLET_STATE_RUN, &(t)->state)) { barrier(); }
+	while (test_bit(TASKLET_STATE_RUN, &(t)->state))
+		cpu_relax();
 }
 #else
 #define tasklet_trylock(t) 1