linux-kernel - Re: [PATCH] ftrace: add tracing_thresh support to function

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Message-ID: <20100227102556.GE5130@nowhere>
Date:	Sat, 27 Feb 2010 11:25:58 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Tim Bird <tim.bird@...sony.com>
Cc:	"Bird, Tim" <Timothy.Bird@...sony.com>,
	Steven Rostedt <srostedt@...hat.com>,
	linux kernel <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] ftrace: add tracing_thresh support to function_graph
	tracer (v3)

On Fri, Feb 26, 2010 at 10:27:29AM -0800, Tim Bird wrote:
> On 02/25/2010 06:46 PM, Frederic Weisbecker wrote:
> >> +static int __init set_tracing_thresh(char *str)
> >> +{
> >> +	unsigned long threshhold;
> >> +	int ret;
> >> +
> >> +	if (!str)
> >> +		return 0;
> >> +	ret = strict_strtoul(str, 0, &threshhold);
> >> +	if (ret < 0)
> >> +		return 0;
> >> +	tracing_thresh = threshhold * 1000;
> >> +	return 1;
> >> +}
> >> +__setup("tracing_thresh=", set_tracing_thresh);
> > 
> > Looks like setting this, while the function graph tracer (normal
> > mode) is running, will have no effect. That said it's perfectly
> > fine as it would be pointless to change this value in the middle
> > of the tracing.
> > 
> The command line is parsed before the tracer is activated, so
> tracing_thresh is set when trace_graph_init() is called, which
> results in the desired behaviour (that is, if you specify the
> tracing_thresh on the command line, you get the duration
> filtering on bootup).


Oh right, I made a confusion with the tracing_thresh file
write callback.

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