tracing: Explain about unstable clock on resume with ring buffer warning (31274d72) · Commits · 戴 / test

The "Delta way too big" warning might appear on a system with a unstable shed clock right after the system is resumed and tracing was enabled at time of suspend. Since it's not realy a bug, and the unstable sched clock is working fast and reliable otherwise, Steven suggested to keep using the sched clock in any case and just to make note in the warning itself. v2 changes: - added #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK Signed-off-by:

Jiri Olsa <jolsa@redhat.com> LKML-Reference: <20110218145219.GD2604@jolsa.brq.redhat.com> Signed-off-by:

Steven Rostedt <rostedt@goodmis.org>

kernel/trace/ring_buffer.c

+10 −2

Original line number	Diff line number	Diff line
		@@ -2172,11 +2172,19 @@ rb_reserve_next_event(struct ring_buffer *buffer,
		if (likely(ts >= cpu_buffer->write_stamp)) {
		delta = diff;
		if (unlikely(test_time_stamp(delta))) {
		int local_clock_stable = 1;
		#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
		local_clock_stable = sched_clock_stable;
		#endif
		WARN_ONCE(delta > (1ULL << 59),
		KERN_WARNING "Delta way too big! %llu ts=%llu write stamp = %llu\n",
		KERN_WARNING "Delta way too big! %llu ts=%llu write stamp = %llu\n%s",
		(unsigned long long)delta,
		(unsigned long long)ts,
		(unsigned long long)cpu_buffer->write_stamp);
		(unsigned long long)cpu_buffer->write_stamp,
		local_clock_stable ? "" :
		"If you just came from a suspend/resume,\n"
		"please switch to the trace global clock:\n"
		" echo global > /sys/kernel/debug/tracing/trace_clock\n");
		add_timestamp = 1;
		}
		}

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