67 lines
2.2 KiB
Diff
67 lines
2.2 KiB
Diff
|
From b46f8c74afdd30cd52bfdcc2231470a0bab04416 Mon Sep 17 00:00:00 2001
|
||
|
|
From: James Hogan <james.hogan@imgtec.com>
|
||
|
|
Date: Fri, 22 Apr 2016 18:22:45 +0100
|
||
|
|
Subject: clockevents: Retry programming min delta up to 10 times
|
||
|
|
|
||
|
|
Under virtualisation it is possible to get unexpected latency during a
|
||
|
|
clockevent device's set_next_event() callback which can make it return
|
||
|
|
-ETIME even for a delta based on min_delta_ns.
|
||
|
|
|
||
|
|
The clockevents_program_min_delta() implementation for
|
||
|
|
CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST=n doesn't handle retries when this
|
||
|
|
happens, nor does clockevents_program_event() or its callers when force
|
||
|
|
is true (for example hrtimer_reprogram()). This can result in hangs
|
||
|
|
until the clock event device does a full period.
|
||
|
|
|
||
|
|
It isn't appropriate to use MIN_ADJUST in this case as occasional
|
||
|
|
hypervisor induced high latency will cause min_delta_ns to quickly
|
||
|
|
increase to the maximum.
|
||
|
|
Instead, borrow the retry pattern from the MIN_ADJUST case, but without
|
||
|
|
making adjustments. We retry up to 10 times before giving up.
|
||
|
|
|
||
|
|
(picked https://patchwork.kernel.org/patch/8909491/)
|
||
|
|
|
||
|
|
Signed-off-by: James Hogan <james.hogan@imgtec.com>
|
||
|
|
---
|
||
|
|
kernel/time/clockevents.c | 26 +++++++++++++++++++-------
|
||
|
|
1 file changed, 19 insertions(+), 7 deletions(-)
|
||
|
|
|
||
|
|
--- a/kernel/time/clockevents.c
|
||
|
|
+++ b/kernel/time/clockevents.c
|
||
|
|
@@ -281,16 +281,28 @@ static int clockevents_program_min_delta
|
||
|
|
{
|
||
|
|
unsigned long long clc;
|
||
|
|
int64_t delta;
|
||
|
|
+ int i;
|
||
|
|
|
||
|
|
- delta = dev->min_delta_ns;
|
||
|
|
- dev->next_event = ktime_add_ns(ktime_get(), delta);
|
||
|
|
+ for (i = 0;;) {
|
||
|
|
+ delta = dev->min_delta_ns;
|
||
|
|
+ dev->next_event = ktime_add_ns(ktime_get(), delta);
|
||
|
|
|
||
|
|
- if (clockevent_state_shutdown(dev))
|
||
|
|
- return 0;
|
||
|
|
+ if (clockevent_state_shutdown(dev))
|
||
|
|
+ return 0;
|
||
|
|
|
||
|
|
- dev->retries++;
|
||
|
|
- clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
|
||
|
|
- return dev->set_next_event((unsigned long) clc, dev);
|
||
|
|
+ dev->retries++;
|
||
|
|
+ clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
|
||
|
|
+ if (dev->set_next_event((unsigned long) clc, dev) == 0)
|
||
|
|
+ return 0;
|
||
|
|
+
|
||
|
|
+ if (++i > 9) {
|
||
|
|
+ /*
|
||
|
|
+ * We tried 10 times to program the device with the
|
||
|
|
+ * given min_delta_ns. Get out of here.
|
||
|
|
+ */
|
||
|
|
+ return -ETIME;
|
||
|
|
+ }
|
||
|
|
+ }
|
||
|
|
}
|
||
|
|
|
||
|
|
#endif /* CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST */
|