linux-kernel - [patch 17/19] softirq: Replace barrier() with cpu_relax() in tasklet_unlock

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Message-Id: <20201113141734.660734753@linutronix.de>
Date:   Fri, 13 Nov 2020 15:02:24 +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>,
        Arnd Bergmann <arnd@...db.de>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Helge Deller <deller@....de>, linux-parisc@...r.kernel.org,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>, linux-sh@...r.kernel.org,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        linux-um@...ts.infradead.org, Russell King <linux@...linux.org.uk>,
        Marc Zyngier <maz@...nel.org>,
        Valentin Schneider <valentin.schneider@....com>,
        linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Subject: [patch 17/19] softirq: 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>
---
 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