linux-kernel - Re: [PATCH 4/9 - v2][RFC] tracing: Move fields from event to class structure

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Message-ID: <20100507044914.GE8069@nowhere>
Date:	Fri, 7 May 2010 06:49:16 +0200
From:	Frederic Weisbecker <fweisbec@...il.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>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Christoph Hellwig <hch@....de>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Tom Zanussi <tzanussi@...il.com>
Subject: Re: [PATCH 4/9 - v2][RFC] tracing: Move fields from event to class
	structure

On Mon, May 03, 2010 at 11:40:49PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@...hat.com>
> 
> Move the defined fields from the event to the class structure.
> Since the fields of the event are defined by the class they belong
> to, it makes sense to have the class hold the information instead
> of the individual events. The events of the same class would just
> hold duplicate information.
> 
> After this change the size of the kernel dropped another 8K:
> 
>    text	   data	    bss	    dec	    hex	filename
> 5788186	1337252	9351592	16477030	 fb6b66	vmlinux.orig
> 5774316	1306580	9351592	16432488	 fabd68	vmlinux.reg
> 5774503	1297492	9351592	16423587	 fa9aa3	vmlinux.fields
> 
> Although the text increased, this was mainly due to the C files
> having to adapt to the change. This is a constant increase, where
> new tracepoints will not increase the Text. But the big drop is
> in the data size (as well as needed allocations to hold the fields).
> This will give even more savings as more tracepoints are created.
> 
> Note, if just TRACE_EVENT()s are used and not DECLARE_EVENT_CLASS()
> with several DEFINE_EVENT()s, then the savings will be lost. But
> we are pushing developers to consolidate events with DEFINE_EVENT()
> so this should not be an issue.
> 
> The kprobes define a unique class to every new event, but are dynamic
> so it should not be a issue.
> 
> The syscalls however have a single class but the fields for the individual
> events are different. The syscalls use a metadata to define the
> fields. I moved the fields list from the event to the metadata and
> added a "get_fields()" function to the class. This function is used
> to find the fields. For normal events and kprobes, get_fields() just
> returns a pointer to the fields list_head in the class. For syscall
> events, it returns the fields list_head in the metadata for the event.
> 
> v2:  Fixed the syscall fields. The syscall metadata needs a list
>      of fields for both enter and exit.
> 
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Cc: Masami Hiramatsu <mhiramat@...hat.com>
> Cc: Tom Zanussi <tzanussi@...il.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>


Acked-by: Frederic Weisbecker <fweisbec@...il.com>

Now I need to recover from my CPP headache before reviewing
this set further ;)

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