linux-kernel - [tip: irq/core] tasklets: Replace barrier() with cpu_relax() in tasklet_unlock

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Date:   Wed, 17 Mar 2021 15:49:00 -0000
From:   "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, maz@...nel.org
Subject: [tip: irq/core] tasklets: Replace barrier() with cpu_relax() in
 tasklet_unlock_wait()

The following commit has been merged into the irq/core branch of tip:

Commit-ID:     d2da74d1278a1b51ef18beafa9da770f0db1c617
Gitweb:        https://git.kernel.org/tip/d2da74d1278a1b51ef18beafa9da770f0db1c617
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Tue, 09 Mar 2021 09:42:04 +01:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Wed, 17 Mar 2021 16:33:51 +01:00

tasklets: Replace barrier() with cpu_relax() in tasklet_unlock_wait()

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>
Tested-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lore.kernel.org/r/20210309084241.249343366@linutronix.de

---
 include/linux/interrupt.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 2b98156..d689fd7 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -672,7 +672,8 @@ static inline void tasklet_unlock(struct tasklet_struct *t)
 
 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