linux-kernel - [patch 01/14] tasklets: Replace barrier() with cpu_relax() in tasklet_unlock

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Message-Id: <20210309084241.249343366@linutronix.de>
Date:   Tue, 09 Mar 2021 09:42:04 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Denis Kirjanov <kda@...ux-powerpc.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        ath9k-devel@....qualcomm.com, Kalle Valo <kvalo@...eaurora.org>,
        linux-wireless@...r.kernel.org, Chas Williams <3chas3@...il.com>,
        linux-atm-general@...ts.sourceforge.net,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-hyperv@...r.kernel.org, linux-pci@...r.kernel.org,
        Stefan Richter <stefanr@...6.in-berlin.de>,
        linux1394-devel@...ts.sourceforge.net
Subject: [patch 01/14] 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>
---
 include/linux/interrupt.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -672,7 +672,8 @@ 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