diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2021-03-09 09:42:08 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2021-03-17 16:33:55 +0100 |
| commit | da044747401fc16202e223c9da970ed4e84fd84d (patch) | |
| tree | 66be6307684a35671cfefc813a2cd2c61e5ff48e | |
| parent | b0cd02c2a9494dbf0a1cc7dc7a3b8b400c158d37 (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
| -rw-r--r-- | include/linux/interrupt.h | 13 | ||||
| -rw-r--r-- | kernel/softirq.c | 18 |
2 files changed, 20 insertions, 11 deletions
diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h index b7f00121f124..b50be4fbbc98 100644 --- a/include/linux/interrupt.h +++ b/include/linux/interrupt.h @@ -664,17 +664,8 @@ static inline int tasklet_trylock(struct tasklet_struct *t) return !test_and_set_bit(TASKLET_STATE_RUN, &(t)->state); } -static inline void tasklet_unlock(struct tasklet_struct *t) -{ - smp_mb__before_atomic(); - clear_bit(TASKLET_STATE_RUN, &(t)->state); -} - -static inline void tasklet_unlock_wait(struct tasklet_struct *t) -{ - while (test_bit(TASKLET_STATE_RUN, &t->state)) - cpu_relax(); -} +void tasklet_unlock(struct tasklet_struct *t); +void tasklet_unlock_wait(struct tasklet_struct *t); /* * Do not use in new code. Waiting for tasklets from atomic contexts is 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; |