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authorPeter Zijlstra <peterz@infradead.org>2021-03-09 09:42:08 +0100
committerThomas Gleixner <tglx@linutronix.de>2021-03-17 16:33:55 +0100
commitda044747401fc16202e223c9da970ed4e84fd84d (patch)
tree66be6307684a35671cfefc813a2cd2c61e5ff48e /kernel/softirq.c
parentb0cd02c2a9494dbf0a1cc7dc7a3b8b400c158d37 (diff)
tasklets: Replace spin wait in tasklet_unlock_wait()
tasklet_unlock_wait() spin waits for TASKLET_STATE_RUN to be cleared. This is wasting CPU cycles in a tight loop which is especially painful in a guest when the CPU running the tasklet is scheduled out. tasklet_unlock_wait() is invoked from tasklet_kill() which is used in teardown paths and not performance critical at all. Replace the spin wait with wait_var_event(). There are no users of tasklet_unlock_wait() which are invoked from atomic contexts. The usage in tasklet_disable() has been replaced temporarily with the spin waiting variant until the atomic users are fixed up and will be converted to the sleep wait variant later. Signed-off-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20210309084241.783936921@linutronix.de
Diffstat (limited to 'kernel/softirq.c')
-rw-r--r--kernel/softirq.c18
1 files changed, 18 insertions, 0 deletions
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 8d56bbf852ea..ef6429a33883 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -25,6 +25,7 @@
#include <linux/smpboot.h>
#include <linux/tick.h>
#include <linux/irq.h>
+#include <linux/wait_bit.h>
#include <asm/softirq_stack.h>
@@ -632,6 +633,23 @@ void tasklet_kill(struct tasklet_struct *t)
}
EXPORT_SYMBOL(tasklet_kill);
+#ifdef CONFIG_SMP
+void tasklet_unlock(struct tasklet_struct *t)
+{
+ smp_mb__before_atomic();
+ clear_bit(TASKLET_STATE_RUN, &t->state);
+ smp_mb__after_atomic();
+ wake_up_var(&t->state);
+}
+EXPORT_SYMBOL_GPL(tasklet_unlock);
+
+void tasklet_unlock_wait(struct tasklet_struct *t)
+{
+ wait_var_event(&t->state, !test_bit(TASKLET_STATE_RUN, &t->state));
+}
+EXPORT_SYMBOL_GPL(tasklet_unlock_wait);
+#endif
+
void __init softirq_init(void)
{
int cpu;