The following commit has been merged into the sched/core branch of tip:
Commit-ID: 52103be07d8b08311955f8c30e535c2dda290cf4
Gitweb: https://git.kernel.org/tip/52103be07d8b08311955f8c30e535c2dda290cf4
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Tue, 26 May 2020 18:10:59 +02:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Thu, 28 May 2020 10:54:15 +02:00
smp: Optimize flush_smp_call_function_queue()
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@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20200526161907.836818381@xxxxxxxxxxxxx
---
kernel/smp.c | 27 +++++++++++++++++++++++----
1 file changed, 23 insertions(+), 4 deletions(-)
diff --git a/kernel/smp.c b/kernel/smp.c
index 786092a..db2f738 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -209,9 +209,9 @@ void generic_smp_call_function_single_interrupt(void)
*/
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;
+ struct llist_node *entry, *prev;
+ struct llist_head *head;
static bool warned;
lockdep_assert_irqs_disabled();
@@ -235,21 +235,40 @@ static void flush_smp_call_function_queue(bool warn_cpu_offline)
csd->func);
}
+ /*
+ * First; run all SYNC callbacks, people are waiting for us.
+ */
+ prev = NULL;
llist_for_each_entry_safe(csd, csd_next, entry, llist) {
smp_call_func_t func = csd->func;
void *info = csd->info;
/* Do we wait until *after* callback? */
if (csd->flags & CSD_FLAG_SYNCHRONOUS) {
+ if (prev) {
+ prev->next = &csd_next->llist;
+ } else {
+ entry = &csd_next->llist;
+ }
func(info);
csd_unlock(csd);
} else {
- csd_unlock(csd);
- func(info);
+ prev = &csd->llist;
}
}
/*
+ * 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().
* Smp functions above are typically synchronous so they
* better run first since some other CPUs may be busy waiting
|