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authorJames Hogan <jhogan@kernel.org>2017-10-19 15:17:23 +0100
committerThomas Gleixner <tglx@linutronix.de>2017-10-19 16:29:15 +0200
commit3a29ddb1c5986a6d3f941bfb1f434105203ce7f6 (patch)
tree2dc9c5b3f1280e5459e0f9076a2c4362c3ed56c8 /kernel/time
parentba16490eac146ebb178017e5de3d61c645552fab (diff)
downloadlinux-3a29ddb1c5986a6d3f941bfb1f434105203ce7f6.tar.bz2
clockevents: Retry programming min delta up to 10 times
When CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST=n, the call path hrtimer_reprogram -> clockevents_program_event -> clockevents_program_min_delta will not retry if the clock event driver returns -ETIME. If the driver could not satisfy the program_min_delta for any reason, the lack of a retry means the CPU may not receive a tick interrupt, potentially until the counter does a full period. This leads to rcu_sched timeout messages as the stalled CPU is detected by other CPUs, and other issues if the CPU is holding locks or other resources at the point at which it stalls. There have been a couple of observed mechanisms through which a clock event driver could not satisfy the requested min_delta and return -ETIME. With the MIPS GIC driver, the shared execution resource within MT cores means inconventient latency due to execution of instructions from other hardware threads in the core, within gic_next_event, can result in an event being set in the past. Additionally 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. It isn't appropriate to use MIN_ADJUST in the virtualisation 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. Retry up to 10 times, each time increasing the attempted delta by min_delta, before giving up. [ Matt: Reworked the loop and made retry increase the delta. ] Signed-off-by: James Hogan <jhogan@kernel.org> Signed-off-by: Matt Redfearn <matt.redfearn@mips.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: linux-mips@linux-mips.org Cc: Daniel Lezcano <daniel.lezcano@linaro.org> Cc: "Martin Schwidefsky" <schwidefsky@de.ibm.com> Cc: James Hogan <james.hogan@mips.com> Link: https://lkml.kernel.org/r/1508422643-6075-1-git-send-email-matt.redfearn@mips.com
Diffstat (limited to 'kernel/time')
-rw-r--r--kernel/time/clockevents.c21
1 files changed, 13 insertions, 8 deletions
diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index 4237e0744e26..16c027e9cc73 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -280,17 +280,22 @@ static int clockevents_program_min_delta(struct clock_event_device *dev)
static int clockevents_program_min_delta(struct clock_event_device *dev)
{
unsigned long long clc;
- int64_t delta;
+ int64_t delta = 0;
+ int i;
- delta = dev->min_delta_ns;
- dev->next_event = ktime_add_ns(ktime_get(), delta);
+ for (i = 0; i < 10; i++) {
+ 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;
+ }
+ return -ETIME;
}
#endif /* CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST */