Subject: Re: [patch 4/5] x86, ftrace, hw-branch-tracer: reset trace on close
From: Steven Rostedt <srostedt@redhat.com>
To: Markus Metzger <markus.t.metzger@intel.com>
Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, tglx@linutronix.de,
       hpa@zytor.com, markus.t.metzger@gmail.com
In-Reply-To: <20090116120153.A30291@sedona.ch.intel.com>
References: <20090116120153.A30291@sedona.ch.intel.com>
Content-Type: text/plain
Organization: Red Hat
Date: Fri, 16 Jan 2009 10:01:30 -0500
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On Fri, 2009-01-16 at 12:01 +0100, Markus Metzger wrote:
> Reset the ftrace buffer on close. Since we use cyclic buffers to store
> the trace, the trace is not contiguous, anyway. This behaviour should
> be more natural.

So you want multiple reads of /debug/tracing/trace to return different
output? Kind of like the trace_pipe? But trace_pipe is a real consumer.

> 
> Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
> ---
> 
> Index: ftrace/kernel/trace/trace_hw_branches.c
> ===================================================================
> --- ftrace.orig/kernel/trace/trace_hw_branches.c	2009-01-14 15:26:11.000000000 +0100
> +++ ftrace/kernel/trace/trace_hw_branches.c	2009-01-14 15:26:16.000000000 +0100
> @@ -272,6 +272,11 @@
>  	mutex_unlock(&bts_tracer_mutex);
>  }
>  
> +static void trace_bts_close(struct trace_iterator *iter)
> +{
> +	tracing_reset_online_cpus(iter->tr);
> +}
> +
>  void trace_hw_branch_oops(void)
>  {
>  	mutex_lock(&bts_tracer_mutex);
> @@ -290,7 +295,8 @@

BTW, can you run your diff with the -p option. This will help in knowing
which function the change is in. There's some hunks where it is
ambiguous. If you use quilt, you can add:

  QUILT_DIFF_OPTS='-p'

to you .quiltrc file.

-- Steve


>  	.print_line	= bts_trace_print_line,
>  	.start		= bts_trace_start,
>  	.stop		= bts_trace_stop,
> -	.open		= trace_bts_prepare
> +	.open		= trace_bts_prepare,
> +	.close		= trace_bts_close
>  };
>  
>  __init static int init_bts_trace(void)
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