linux-kernel - [PATCH 2/5] tracing/events: change the type of __str_loc

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Date:	Tue, 26 May 2009 04:04:47 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Zhaolei <zhaolei@...fujitsu.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: [PATCH 2/5] tracing/events: change the type of __str_loc_item to unsigned short

From: Li Zefan <lizf@...fujitsu.com>

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>
Cc: Steven Rostedt <rostedt@...dmis.org>
LKML-Reference: <4A14EDB6.2050507@...fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.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
-- 
1.6.2.3

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