linux-kernel - [PATCH] firewire: reorder struct fw

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Date:	Sat, 29 Nov 2008 19:00:56 +0100 (CET)
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	linux1394-devel@...ts.sourceforge.net
cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] firewire: reorder struct fw_card for better cache efficiency

topology_map is by far the largest member in struct fw_card.  Move it to
the very end of the struct so that card pointer dereferences have better
chances to hit the CPU cache.

This requires to increase the topology_map backing store to the size
specified in IEEE 1394, i.e. 256 rather than 255 quadlets.  Otherwise
the topology_map response handler may access invalid memory.

Signed-off-by: Stefan Richter <stefanr@...6.in-berlin.de>
---
 drivers/firewire/fw-transaction.h |   10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

Index: linux/drivers/firewire/fw-transaction.h
===================================================================
--- linux.orig/drivers/firewire/fw-transaction.h
+++ linux/drivers/firewire/fw-transaction.h
@@ -235,13 +235,6 @@ struct fw_card {
 	int link_speed;
 	int config_rom_generation;
 
-	/*
-	 * We need to store up to 4 self ID for a maximum of 63
-	 * devices plus 3 words for the topology map header.
-	 */
-	u32 topology_map[252 + 3];
-	u32 broadcast_channel;
-
 	spinlock_t lock; /* Take this lock when handling the lists in
 			  * this struct. */
 	struct fw_node *local_node;
@@ -259,6 +252,9 @@ struct fw_card {
 	struct delayed_work work;
 	int bm_retries;
 	int bm_generation;
+
+	u32 broadcast_channel;
+	u32 topology_map[(CSR_TOPOLOGY_MAP_END - CSR_TOPOLOGY_MAP) / 4];
 };
 
 static inline struct fw_card *fw_card_get(struct fw_card *card)

-- 
Stefan Richter
-=====-==--- =-== ===-=
http://arcgraph.de/sr/

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