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