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

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Message-ID: <4FC8BAF5.5050008@hitachi.com>
Date:	Fri, 01 Jun 2012 21:52:05 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Steven Rostedt <rostedt@...dmis.org>
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: [PATCH 1/5] ftrace: Synchronize variable setting with breakpoints

(2012/06/01 20:37), Steven Rostedt wrote:
> 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.

That's reasonable for me :). You can feel free to change/remove
text_poke_smp_batch which is already old-style interface.

Thanks!

-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com
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