From b46f8c74afdd30cd52bfdcc2231470a0bab04416 Mon Sep 17 00:00:00 2001 From: James Hogan 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 --- 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 */