linux-kernel - Re: [PATCHv2] trace: adding unstable sched clock note to the warning

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Date:	Mon, 7 Mar 2011 11:45:13 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	rostedt@...dmis.org
Cc:	linux-kernel@...r.kernel.org, fweisbec@...il.com, mingo@...e.hu
Subject: Re: [PATCHv2] trace: adding unstable sched clock note to the warning

hi,
any feedback?

thanks,
jirka

On Fri, Feb 18, 2011 at 03:52:19PM +0100, Jiri Olsa wrote:
> hi,
> 
> warning "Delta way too big" warning might appear on a system with
> unstable shed clock right after the system is resumed and tracing
> was enabled during the suspend.
> 
> Since it's not realy 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 CONFIG_HAVE_UNSTABLE_SCHED_CLOCK dependency
> 
> wbr,
> jirka
> 
> 
> Signed-off-by: Jiri Olsa <jolsa@...hat.com>
> ---
>  kernel/trace/ring_buffer.c |   12 ++++++++++--
>  1 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index bd1c35a..37c4d3e 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -2162,11 +2162,19 @@ 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;
>  		}
>  	}
> -- 
> 1.7.1
> --
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