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authorJohn Stultz <john.stultz@linaro.org>2015-03-11 21:16:32 -0700
committerIngo Molnar <mingo@kernel.org>2015-03-13 08:06:58 +0100
commit3c17ad19f0697ffe5ef7438cdafc2d2b7757d8a5 (patch)
tree9d47ff591a06ab8ed93df330b01964da3fbff8d7 /kernel/time/timekeeping.c
parentfb82fe2fe8588745edd73aa3a6229facac5c1e15 (diff)
downloadlinux-3c17ad19f0697ffe5ef7438cdafc2d2b7757d8a5.tar.bz2
timekeeping: Add debugging checks to warn if we see delays
Recently there's been requests for better sanity checking in the time code, so that it's more clear when something is going wrong, since timekeeping issues could manifest in a large number of strange ways in various subsystems. Thus, this patch adds some extra infrastructure to add a check to update_wall_time() to print two new warnings: 1) if we see the call delayed beyond the 'max_cycles' overflow point, 2) or if we see the call delayed beyond the clocksource's 'max_idle_ns' value, which is currently 50% of the overflow point. This extra infrastructure is conditional on a new CONFIG_DEBUG_TIMEKEEPING option, also added in this patch - default off. Tested this a bit by halting qemu for specified lengths of time to trigger the warnings. Signed-off-by: John Stultz <john.stultz@linaro.org> Cc: Dave Jones <davej@codemonkey.org.uk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Prarit Bhargava <prarit@redhat.com> Cc: Richard Cochran <richardcochran@gmail.com> Cc: Stephen Boyd <sboyd@codeaurora.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1426133800-29329-5-git-send-email-john.stultz@linaro.org [ Improved the changelog and the messages a bit. ] Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/time/timekeeping.c')
-rw-r--r--kernel/time/timekeeping.c28
1 files changed, 28 insertions, 0 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 91db94136c10..acf049144cf6 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -118,6 +118,31 @@ static inline void tk_update_sleep_time(struct timekeeper *tk, ktime_t delta)
tk->offs_boot = ktime_add(tk->offs_boot, delta);
}
+#ifdef CONFIG_DEBUG_TIMEKEEPING
+static void timekeeping_check_update(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_deferred("WARNING: timekeeping: Cycle offset (%lld) is larger than allowed by the '%s' clock's max_cycles value (%lld): time overflow\n",
+ offset, name, max_cycles);
+ printk_deferred(" timekeeping: Your kernel is sick, but tries to cope\n");
+ } else {
+ if (offset > (max_cycles >> 1)) {
+ printk_deferred("INFO: timekeeping: Cycle offset (%lld) is larger than the the '%s' clock's 50%% safety margin (%lld)\n",
+ offset, name, max_cycles >> 1);
+ printk_deferred(" timekeeping: Your kernel is still fine, but is feeling a bit nervous\n");
+ }
+ }
+}
+#else
+static inline void timekeeping_check_update(struct timekeeper *tk, cycle_t offset)
+{
+}
+#endif
+
/**
* tk_setup_internals - Set up internals to use clocksource clock.
*
@@ -1630,6 +1655,9 @@ void update_wall_time(void)
if (offset < real_tk->cycle_interval)
goto out;
+ /* Do some additional sanity checking */
+ timekeeping_check_update(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,