linux-kernel - Re: [PATCH] tracing/events: change the type of __str_loc

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Date:	Sun, 24 May 2009 22:31:51 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/events: change the type of __str_loc_item to
	unsigned short

On Thu, May 21, 2009 at 01:59:18PM +0800, Li Zefan wrote:
> When defining a dynamic size string, we add __str_loc_##item to the
> trace entry, and it stores the location of the actual string in
> entry->_str_data[]
> 
> 'unsigned short' should be sufficient to store this information, thus
> we save 2 bytes per dyn-size string in the ring buffer.
> 
> [ Impact: reduce memory occupied by dyn-size strings in ring buffer ]
> 
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> ---
>  include/trace/ftrace.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
> index edb02bc..b5ff2e8 100644
> --- a/include/trace/ftrace.h
> +++ b/include/trace/ftrace.h
> @@ -25,7 +25,7 @@
>  #define __field(type, item)		type	item;
>  
>  #undef __string
> -#define __string(item, src)		int	__str_loc_##item;
> +#define __string(item, src)		unsigned short	__str_loc_##item;
>  
>  #undef TP_STRUCT__entry
>  #define TP_STRUCT__entry(args...) args
> -- 1.5.4.rc3 


Yeah, a max length of about 32000 is sufficient, the filter
engine is bounded to MAX_FILTER_STR_VAL anyway :)

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

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