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

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Date:	Mon, 07 Mar 2011 21:06:38 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	linux-kernel@...r.kernel.org, fweisbec@...il.com, mingo@...e.hu
Subject: Re: [PATCHv2] trace: adding unstable sched clock note to the
 warning

On Mon, 2011-03-07 at 11:45 +0100, Jiri Olsa wrote:
> hi,
> any feedback?

I could pull it in.

Thanks,

-- Steve

> 
> 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
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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> > Please read the FAQ at  http://www.tux.org/lkml/


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