linux-kernel - Re: [PATCH v2 1/8] x86: speed up int3-based patching using less paranoid write

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Date:	Fri, 8 Nov 2013 07:43:36 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Petr Mladek <pmladek@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jiri Kosina <jkosina@...e.cz>, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH v2 1/8] x86: speed up int3-based patching using less
 paranoid write

On Fri, 08 Nov 2013 21:04:26 +0900
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:

> (2013/11/08 18:12), Petr Mladek wrote:
> > This change is inspired by the int3-based patching code used in
> > ftrace. See the commit fd4363fff3d9 (x86: Introduce int3
> > (breakpoint)-based instruction patching).
> > 
> > When trying to use text_poke_bp in ftrace, the result was slower than
> > the original implementation.
> > 
> > It turned out that one difference was in text_poke vs. ftrace_write.
> > text_poke did many extra operations to make sure that the change
> > was atomic.
> 
> AFAIK, the main reason why text_poke is used is avoiding
> RODATA protection (by alias mapping).

That is correct, and the reason ftrace didn't do that is because it
would be quite expensive to map 22,000 addresses for each change.

-- Steve
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