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68 lines
2.1 KiB
Diff
68 lines
2.1 KiB
Diff
From: Peter Zijlstra <peterz@infradead.org>
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Date: Tue, 9 Mar 2021 09:42:09 +0100
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Subject: [PATCH 06/20] tasklets: Replace spin wait in tasklet_kill()
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tasklet_kill() spin waits for TASKLET_STATE_SCHED to be cleared invoking
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yield() from inside the loop. yield() is an ill defined mechanism and the
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result might still be wasting CPU cycles in a tight loop which is
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especially painful in a guest when the CPU running the tasklet is scheduled
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out.
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tasklet_kill() is used in teardown paths and not performance critical at
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all. Replace the spin wait with wait_var_event().
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Signed-off-by: Peter Zijlstra <peterz@infradead.org>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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kernel/softirq.c | 23 +++++++++++++++--------
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1 file changed, 15 insertions(+), 8 deletions(-)
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--- a/kernel/softirq.c
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+++ b/kernel/softirq.c
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@@ -530,6 +530,16 @@ void __tasklet_hi_schedule(struct taskle
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}
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EXPORT_SYMBOL(__tasklet_hi_schedule);
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+static inline bool tasklet_clear_sched(struct tasklet_struct *t)
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+{
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+ if (test_and_clear_bit(TASKLET_STATE_SCHED, &t->state)) {
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+ wake_up_var(&t->state);
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+ return true;
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+ }
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+
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+ return false;
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+}
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+
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static void tasklet_action_common(struct softirq_action *a,
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struct tasklet_head *tl_head,
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unsigned int softirq_nr)
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@@ -549,8 +559,7 @@ static void tasklet_action_common(struct
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if (tasklet_trylock(t)) {
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if (!atomic_read(&t->count)) {
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- if (!test_and_clear_bit(TASKLET_STATE_SCHED,
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- &t->state))
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+ if (!tasklet_clear_sched(t))
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BUG();
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if (t->use_callback)
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t->callback(t);
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@@ -610,13 +619,11 @@ void tasklet_kill(struct tasklet_struct
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if (in_interrupt())
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pr_notice("Attempt to kill tasklet from interrupt\n");
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- while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
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- do {
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- yield();
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- } while (test_bit(TASKLET_STATE_SCHED, &t->state));
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- }
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+ while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state))
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+ wait_var_event(&t->state, !test_bit(TASKLET_STATE_SCHED, &t->state));
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+
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tasklet_unlock_wait(t);
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- clear_bit(TASKLET_STATE_SCHED, &t->state);
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+ tasklet_clear_sched(t);
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}
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EXPORT_SYMBOL(tasklet_kill);
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