The following commit has been merged into the irq/core branch of tip: Commit-ID: 697d8c63c4a2991a22a896a5e6adcdbb28fefe56 Gitweb: https://git.kernel.org/tip/697d8c63c4a2991a22a896a5e6adcdbb28fefe56 Author: Peter Zijlstra <pet...@infradead.org> AuthorDate: Tue, 09 Mar 2021 09:42:09 +01:00 Committer: Thomas Gleixner <t...@linutronix.de> CommitterDate: Wed, 17 Mar 2021 16:33:57 +01:00
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 <pet...@infradead.org> Signed-off-by: Thomas Gleixner <t...@linutronix.de> Acked-by: Peter Zijlstra (Intel) <pet...@infradead.org> Link: https://lore.kernel.org/r/20210309084241.890532...@linutronix.de --- kernel/softirq.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-) diff --git a/kernel/softirq.c b/kernel/softirq.c index ef6429a..ba89ca7 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);
