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| author | Peter Zijlstra <peterz@infradead.org> | 2021-03-09 09:42:09 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2021-03-17 16:33:57 +0100 |
| commit | 697d8c63c4a2991a22a896a5e6adcdbb28fefe56 (patch) | |
| tree | 223efa50042365abc94dcbec5287e94c94773aa0 /kernel/softirq.c | |
| parent | da044747401fc16202e223c9da970ed4e84fd84d (diff) | |
| download | lwn-697d8c63c4a2991a22a896a5e6adcdbb28fefe56.tar.gz lwn-697d8c63c4a2991a22a896a5e6adcdbb28fefe56.zip | |
tasklets: Replace spin wait in tasklet_kill()
tasklet_kill() spin waits for TASKLET_STATE_SCHED to be cleared invoking
yield() from inside the loop. yield() is an ill defined mechanism and the
result might still be wasting CPU cycles in a tight loop which is
especially painful in a guest when the CPU running the tasklet is scheduled
out.
tasklet_kill() is used in teardown paths and not performance critical at
all. Replace the spin wait with wait_var_event().
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/20210309084241.890532921@linutronix.de
Diffstat (limited to 'kernel/softirq.c')
| -rw-r--r-- | kernel/softirq.c | 18 |
1 files changed, 9 insertions, 9 deletions
diff --git a/kernel/softirq.c b/kernel/softirq.c index ef6429a33883..ba89ca77698a 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -532,10 +532,12 @@ void __tasklet_hi_schedule(struct tasklet_struct *t) } EXPORT_SYMBOL(__tasklet_hi_schedule); -static bool tasklet_should_run(struct tasklet_struct *t) +static bool tasklet_clear_sched(struct tasklet_struct *t) { - if (test_and_clear_bit(TASKLET_STATE_SCHED, &t->state)) + if (test_and_clear_bit(TASKLET_STATE_SCHED, &t->state)) { + wake_up_var(&t->state); return true; + } WARN_ONCE(1, "tasklet SCHED state not set: %s %pS\n", t->use_callback ? "callback" : "func", @@ -563,7 +565,7 @@ static void tasklet_action_common(struct softirq_action *a, if (tasklet_trylock(t)) { if (!atomic_read(&t->count)) { - if (tasklet_should_run(t)) { + if (tasklet_clear_sched(t)) { if (t->use_callback) t->callback(t); else @@ -623,13 +625,11 @@ void tasklet_kill(struct tasklet_struct *t) if (in_interrupt()) pr_notice("Attempt to kill tasklet from interrupt\n"); - while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) { - do { - yield(); - } while (test_bit(TASKLET_STATE_SCHED, &t->state)); - } + while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) + wait_var_event(&t->state, !test_bit(TASKLET_STATE_SCHED, &t->state)); + tasklet_unlock_wait(t); - clear_bit(TASKLET_STATE_SCHED, &t->state); + tasklet_clear_sched(t); } EXPORT_SYMBOL(tasklet_kill); |