linux-kernel - Re: [PATCH -tip v3 3/5] x86: Introduce text_poke_smp

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Message-ID: <20100615121804.GA5342@nowhere>
Date:	Tue, 15 Jun 2010 14:18:07 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	Jason Baron <jbaron@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH -tip v3 3/5] x86: Introduce text_poke_smp_batch() for
	batch-code modifying

On Wed, May 19, 2010 at 12:53:26PM -0400, Masami Hiramatsu wrote:
> Introduce text_poke_smp_batch(). This function modifies several
> text areas with one stop_machine() on SMPr. Because calling
> stop_machine() is heavy task, it is better to aggregate text_poke
> requests.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...hat.com>
> Cc: Ananth N Mavinakayanahalli <ananth@...ibm.com>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Jim Keniston <jkenisto@...ibm.com>
> Cc: Jason Baron <jbaron@...hat.com>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
<snip>
> +/**
> + * text_poke_smp_batch - Update instructions on a live kernel on SMP
> + * @params: an array of text_poke parameters
> + * @n: the number of elements in params.
> + *
> + * Modify multi-byte instruction by using stop_machine() on SMP. Since the
> + * stop_machine() is heavy task, it is better to aggregate text_poke requests
> + * and do it once if possible.
> + *
> + * Note: Must be called under get_online_cpus() and text_mutex.
> + */
> +void __kprobes text_poke_smp_batch(struct text_poke_param *params, int n)
> +{
> +	struct text_poke_params tpp = {.params = params, .nparams = n};
> +
> +	atomic_set(&stop_machine_first, 1);
> +	wrote_text = 0;
> +	stop_machine(stop_machine_text_poke, (void *)&tpp, NULL);
> +}


Looks good. But wouldn't it be even better to get stop_machine()
be able to support batches itself?

We could have stop_machine_queue() and stop_machine_flush(),
stop_machine() would be a shortcut for both, to execute single jobs,
may be that could simplify some code here and there.

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