lkml.org 
[lkml]   [2020]   [May]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[RFC][PATCH 2/7] 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@infradead.org>
---
kernel/smp.c | 27 +++++++++++++++++++++++----
1 file changed, 23 insertions(+), 4 deletions(-)

--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -209,9 +209,9 @@ void generic_smp_call_function_single_in
*/
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_queu
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

\
 
 \ /
  Last update: 2020-05-26 18:25    [W:0.296 / U:0.360 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site