linux-kernel - Re: Re: [PATCH 1/5] ftrace: Synchronize variable setting with breakpoints

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Date:	Fri, 01 Jun 2012 07:37:07 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, Dave Jones <davej@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>,
	acme <acme@...stprotocols.net>, yrl.pp-manager.tt@...achi.com
Subject: Re: Re: [PATCH 1/5] ftrace: Synchronize variable setting with
 breakpoints

On Fri, 2012-06-01 at 13:53 +0900, Masami Hiramatsu wrote:

> Hmm, why don't we have two text_poke interfaces for single and
> batch? As like dyn_ftrace, since modifying massive points takes
> a lot time, so we may have additional kconfig something like
> CONFIG_QUICK_BATCH_TEXT_POKE which switches text area to rw while
> batch text_poke.
> 

I'll be working on patches to consolidate the two after I get everything
else working :-)  I still need to work on the ftrace kprobe stuff too.

I hate having a config option to switch between the two, except for
something that can be there if we find the new approach is buggy (like
we have with lockdep). That may be a solution for this if we don't agree
on one now. That is, bring back stop_machine() when LOCKDEP is enabled.
But that should only be a temporary work around not a true fix.

I have no problem with having most of the modifying code be shared
between text_poke and ftrace. I guess the question is, do we want to do
it only with the FIXMAP or do we want text_poke and ftrace to use the rw
method for large batches. Heck, we can set a limit. If we are going to
update more that 100 locations, we switch the kernel to rw, otherwise we
do the FIXMAP update.

-- Steve

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