Recently there's been some request for better sanity
checking in the time code, so that its more clear
when something is going wrong since timekeeping issues
could manifest in a large number of strange ways with
various subsystems.
Thus, this patch adds some extra infrastructure to
add a check update_wall_time to print warnings if we
see the call delayed beyond the max_cycles overflow
point, or beyond the clocksource max_idle_ns value
which is currently 50% of the overflow point.
Tested this a bit by halting qemu for specified
lengths of time to trigger the warnings.
Cc: Dave Jones <da...@codemonkey.org.uk>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Richard Cochran <richardcoch...@gmail.com>
Cc: Prarit Bhargava <pra...@redhat.com>
Cc: Stephen Boyd <sb...@codeaurora.org>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: John Stultz <john.stu...@linaro.org>
---
kernel/time/jiffies.c | 1 +
kernel/time/timekeeping.c | 18 ++++++++++++++++++
2 files changed, 19 insertions(+)
diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
index a6a5bf5..7e41390 100644
--- a/kernel/time/jiffies.c
+++ b/kernel/time/jiffies.c
@@ -71,6 +71,7 @@ static struct clocksource clocksource_jiffies = {
.mask = 0xffffffff, /*32bits*/
.mult = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */
.shift = JIFFIES_SHIFT,
+ .max_cycles = 10,
};
__cacheline_aligned_in_smp DEFINE_SEQLOCK(jiffies_lock);
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 6a93185..0dcceba 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1319,6 +1319,22 @@ static int __init timekeeping_init_ops(void)
}
device_initcall(timekeeping_init_ops);
+static void timekeeping_check_offset(struct timekeeper *tk, cycle_t offset)
+{
+
+ cycle_t max_cycles = tk->tkr.clock->max_cycles;
+ const char *name = tk->tkr.clock->name;
+
+ if (offset > max_cycles)
+ printk("ERROR: cycle offset (%lld) is larger then"
+ " allowed %s max_cycles (%lld)\n",
+ offset, name, max_cycles);
+ else if (offset > (max_cycles >> 1))
+ printk("WARNING: cycle offset (%lld) is past"
+ " the %s 50%% safety margin (%lld)\n",
+ offset, name, max_cycles>>1);
+}
+
/*
* Apply a multiplier adjustment to the timekeeper
*/
@@ -1602,6 +1618,8 @@ void update_wall_time(void)
if (offset < real_tk->cycle_interval)
goto out;
+ timekeeping_check_offset(real_tk, offset);
+
/*
* With NO_HZ we may have to accumulate many cycle_intervals
* (think "ticks") worth of time at once. To do this efficiently,
--
1.9.1
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
