From: Ingo Molnar <mingo@elte.hu>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
linux-kernel@vger.kernel.org,
Frederic Weisbecker <fweisbec@gmail.com>,
Steven Rostedt <srostedt@redhat.com>
Subject: Re: [PATCH 1/6] ftrace: move function tracer functions out of trace.c
Date: Fri, 16 Jan 2009 12:12:43 +0100 [thread overview]
Message-ID: <20090116111243.GA20082@elte.hu> (raw)
In-Reply-To: <20090115224925.6b0e6c24.akpm@linux-foundation.org>
* Andrew Morton <akpm@linux-foundation.org> wrote:
> On Thu, 15 Jan 2009 23:53:43 -0500 Steven Rostedt <rostedt@goodmis.org> wrote:
>
> > static void
> > +function_trace_call_preempt_only(unsigned long ip, unsigned long parent_ip)
> > +{
> > + struct trace_array *tr = func_trace;
> > + struct trace_array_cpu *data;
> > + unsigned long flags;
> > + long disabled;
> > + int cpu, resched;
> > + int pc;
> > +
> > + if (unlikely(!ftrace_function_enabled))
> > + return;
>
> We're optimizing for the tracing-is-enabled case. What's the thinking
> here?
There's two levels here: first the patched in callsites. Those are NOPs in
the usual case - there's no overhead for the default 'function tracing is
built in but not enabled' case.
There's a second level: a /debug/tracing/tracing_enabled lightweight
dynamic flag to flip tracing on/off while the tracer is enabled. _That_
one, if it ever matters to a codepath, is default-enabled.
I.e. the above code sequence is correct.
Thanks,
Ingo
next prev parent reply other threads:[~2009-01-16 11:13 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-16 4:53 [PATCH 0/6] ftrace: more updates to tip Steven Rostedt
2009-01-16 4:53 ` [PATCH 1/6] ftrace: move function tracer functions out of trace.c Steven Rostedt
2009-01-16 6:49 ` Andrew Morton
2009-01-16 11:12 ` Ingo Molnar [this message]
2009-01-16 13:13 ` Steven Rostedt
2009-01-16 4:53 ` [PATCH 2/6] trace: add gcc printf check to trace_seq_printf Steven Rostedt
2009-01-16 4:53 ` [PATCH 3/6] trace: clean up format errors in calls " Steven Rostedt
2009-01-16 4:53 ` [PATCH 4/6] ftrace: combine stack trace in function call Steven Rostedt
2009-01-16 4:53 ` [PATCH 5/6] ftrace: remove static from function tracer functions Steven Rostedt
2009-01-16 4:53 ` [PATCH 6/6] trace: set max latency variable to zero on default Steven Rostedt
2009-01-16 11:25 ` [PATCH 0/6] ftrace: more updates to tip Ingo Molnar
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