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

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 2b98156ec7075df80ce40d65b0b461d9403fe9c7..d689fd7381522da966222e70f3d5aa4140448a57 100644 (file)
--- 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