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smp: Optimize flush_smp_call_function_queue()

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The call_single_queue can contain (two) different callbacks,
synchronous and asynchronous. The current interrupt handler runs them
in-order, which means that remote CPUs that are waiting for their
synchronous call can be delayed by running asynchronous callbacks.

Rework the interrupt handler to first run the synchonous callbacks.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200526161907.836818381@infradead.org
This commit is contained in:
Peter Zijlstra 2020-05-26 18:10:59 +02:00 • committed by Ingo Molnar
parent 19a1f5ec69
commit 52103be07d
1 changed files with 23 additions and 4 deletions
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27
kernel/smp.c
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@ -209,9 +209,9 @@ void generic_smp_call_function_single_interrupt(void)
*/ */
static void flush_smp_call_function_queue(bool warn_cpu_offline) static void flush_smp_call_function_queue(bool warn_cpu_offline)
{ {
struct llist_head *head;
struct llist_node *entry;
call_single_data_t *csd, *csd_next; call_single_data_t *csd, *csd_next;
struct llist_node *entry, *prev;
struct llist_head *head;
static bool warned; static bool warned;
lockdep_assert_irqs_disabled(); lockdep_assert_irqs_disabled();
@ -235,20 +235,39 @@ static void flush_smp_call_function_queue(bool warn_cpu_offline)
csd->func); csd->func);
} }
/*
* First; run all SYNC callbacks, people are waiting for us.
*/
prev = NULL;
llist_for_each_entry_safe(csd, csd_next, entry, llist) { llist_for_each_entry_safe(csd, csd_next, entry, llist) {
smp_call_func_t func = csd->func; smp_call_func_t func = csd->func;
void *info = csd->info; void *info = csd->info;
/* Do we wait until *after* callback? */ /* Do we wait until *after* callback? */
if (csd->flags & CSD_FLAG_SYNCHRONOUS) { if (csd->flags & CSD_FLAG_SYNCHRONOUS) {
if (prev) {
prev->next = &csd_next->llist;
} else {
entry = &csd_next->llist;
}
func(info); func(info);
csd_unlock(csd); csd_unlock(csd);
} else { } else {
csd_unlock(csd); prev = &csd->llist;
func(info);
} }
} }
/*
* Second; run all !SYNC callbacks.
*/
llist_for_each_entry_safe(csd, csd_next, entry, llist) {
smp_call_func_t func = csd->func;
void *info = csd->info;
csd_unlock(csd);
func(info);
}
/* /*
* Handle irq works queued remotely by irq_work_queue_on(). * Handle irq works queued remotely by irq_work_queue_on().
* Smp functions above are typically synchronous so they * Smp functions above are typically synchronous so they