diff options
Diffstat (limited to 'features/rt/tasklets-Replace-spin-wait-in-tasklet_unlock_wait.patch')
| -rw-r--r-- | features/rt/tasklets-Replace-spin-wait-in-tasklet_unlock_wait.patch | 89 |
1 files changed, 89 insertions, 0 deletions
diff --git a/features/rt/tasklets-Replace-spin-wait-in-tasklet_unlock_wait.patch b/features/rt/tasklets-Replace-spin-wait-in-tasklet_unlock_wait.patch new file mode 100644 index 00000000..edca165f --- /dev/null +++ b/features/rt/tasklets-Replace-spin-wait-in-tasklet_unlock_wait.patch @@ -0,0 +1,89 @@ +From 9c90471b76134571fa2dfddb7423d48c521146ab Mon Sep 17 00:00:00 2001 +From: Peter Zijlstra <peterz@infradead.org> +Date: Tue, 9 Mar 2021 09:42:08 +0100 +Subject: [PATCH 045/191] 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> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + include/linux/interrupt.h | 13 ++----------- + kernel/softirq.c | 18 ++++++++++++++++++ + 2 files changed, 20 insertions(+), 11 deletions(-) + +diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h +index f0b82429950c..ee3ce4f852b7 100644 +--- a/include/linux/interrupt.h ++++ b/include/linux/interrupt.h +@@ -660,17 +660,8 @@ 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 9908ec4a9bfe..7cd63df59e1c 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> + +@@ -621,6 +622,23 @@ 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; +-- +2.19.1 + |