@@ -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);
@@ -118,6 +118,26 @@ 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("ERROR: cycle offset (%lld) is larger then"
+ " allowed %s max_cycles (%lld)\n",
+ offset, name, max_cycles);
+ else if (offset > (max_cycles >> 1))
+ printk_deferred("WARNING: cycle offset (%lld) is past"
+ " the %s 50%% safety margin (%lld)\n",
+ offset, name, max_cycles>>1);
+}
+#else
+#define timekeeping_check_update(x, y)
+#endif
+
/**
* tk_setup_internals - Set up internals to use clocksource clock.
*
@@ -1602,6 +1622,9 @@ 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,
@@ -852,6 +852,18 @@ config SCHED_STACK_END_CHECK
data corruption or a sporadic crash at a later stage once the region
is examined. The runtime overhead introduced is minimal.
+config DEBUG_TIMEKEEPING
+ bool "Enable extra timekeeping sanity checking"
+ help
+ This option will enable additional timekeeping sanity checks
+ which may be helpful when diagnoising issues where timekeeping
+ problems are suspected.
+
+ This may include checks in the timekeeping hotpaths, so this
+ option may have a performance impact to some workloads.
+
+ If unsure, say N.
+
config TIMER_STATS
bool "Collect kernel timers statistics"
depends on DEBUG_KERNEL && PROC_FS
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. This extra infrastructure is conditionalized behind a new CONFIG_DEBUG_TIMEKEEPING option also added in this patch. Tested this a bit by halting qemu for specified lengths of time to trigger the warnings. Cc: Dave Jones <davej@codemonkey.org.uk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Richard Cochran <richardcochran@gmail.com> Cc: Prarit Bhargava <prarit@redhat.com> Cc: Stephen Boyd <sboyd@codeaurora.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: John Stultz <john.stultz@linaro.org> --- kernel/time/jiffies.c | 1 + kernel/time/timekeeping.c | 23 +++++++++++++++++++++++ lib/Kconfig.debug | 12 ++++++++++++ 3 files changed, 36 insertions(+)