linux-kernel - Re: [PATCH][RFC] ftrace: function oprofiler

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Date:	Sat, 25 Oct 2008 09:50:05 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frédéric Weisbecker <fweisbec@...il.com>
cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH][RFC] ftrace: function oprofiler


On Sat, 25 Oct 2008, Fr?d?ric Weisbecker wrote:

> Hi Steven,
> 
> 2008/10/25 Steven Rostedt <rostedt@...dmis.org>:
> > # cat /debug/tracing/ftrace_profile | sort -brn | head -20
> >   280075  : __rcu_read_unlock+0xb/0xa2
> >   280065  : __rcu_read_lock+0x11/0xb3
> 
> The rcu function are on top of this profile. May be it's because you use
> rcu when you touch your hash table.
> Wouldn't be interesting to disable the counter adding for these
> functions when they
> are used at this time?

It is disabled at that time. Look at the trace_active variable. If it
is already set for that CPU, the counter is disabled.

But!  That said. I need to make the count an atomic inc. There's nothing
protecting it from SMP.

> 
> > +config FUNCTION_PROFILER
> > +       bool "Trace max stack"
> 
> Copy-paste error? :-)

Hehe, yeah. This and the above bug are both the cause of writing this 
after midnight. That is exactly why I said this is not ready for inclusion 
;-)

-- Steve

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