linux-kernel - Re: [PATCH 10/10 -v3][RFC] tracing: Combine event filter_active and enable into single flags field

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Message-ID: <20100511033026.GA28162@Krystal>
Date:	Mon, 10 May 2010 23:30:27 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 10/10 -v3][RFC] tracing: Combine event filter_active
	and enable into single flags field

* Steven Rostedt (rostedt@...dmis.org) wrote:
> From: Steven Rostedt <srostedt@...hat.com>
> 
> The filter_active and enable both use an int (4 bytes each) to
> set a single flag. We can save 4 bytes per event by combining the
> two into a single integer.
> 
>    text	   data	    bss	    dec	    hex	filename
> 5788186	1337252	9351592	16477030	 fb6b66	vmlinux.orig
> 5761074	1262596	9351592	16375262	 f9ddde	vmlinux.id
> 5761007	1256916	9351592	16369515	 f9c76b	vmlinux.flags
> 
> This gives us another 5K in savings.
> 
> The modification of both the enable and filter fields are done
> under the event_mutex, so it is still safe to combine the two.
> 
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
[...]
>  struct ftrace_event_call {
>  	struct list_head	list;
>  	struct ftrace_event_class *class;
> @@ -154,8 +164,15 @@ struct ftrace_event_call {
>  	void			*mod;
>  	void			*data;
>  
> -	int			enabled;
> -	int			filter_active;
> +	/*
> +	 * 32 bit flags:
> +	 *   bit 1:		enabled
> +	 *   bit 2:		filter_active
> +	 *
> +	 *  Must hold event_mutex to change.
> +	 */
> +	unsigned int		flags;
> +

I would also comment about flags read-side:

 * Flags are read concurrently without locking.

Besides that minor nit, the whole patchset has my

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

Thanks!

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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