jtag: commands: save a pointer to list tail

By saving a pointer to the tail of the list,
we don't need to traverse the entire command
queue before we're able to append an item to
it.

With this patch, I see a 10% improvement when
using the embedded XDS100v2 on AM437x IDK board
to load a 4MiB binary (linux zImage) to DDR
with load_image.

IOW, we went from ~305kB/sec to ~336kb/sec.

Change-Id: Idb55d49f0d0106043374ab520b2f3b6b32f2c50f
Signed-off-by: Felipe Balbi <balbi@ti.com>
Reviewed-on: http://openocd.zylin.com/2709
Tested-by: jenkins
Reviewed-by: Stian Skjelstad <stian@nixia.no>
Reviewed-by: Daniele Emancipato <daniele12457@hotmail.com>
Reviewed-by: Matthias Welwarsky <matthias@welwarsky.de>
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>

1 files changed, 5 insertions, 3 deletions

diff --git a/src/jtag/commands.c b/src/jtag/commands.c
index 5e06840a..750ebab0 100644
--- a/src/jtag/commands.c
+++ b/src/jtag/commands.c
@@ -36,13 +36,14 @@
 #include "commands.h"
 
 struct cmd_queue_page {
+	struct cmd_queue_page *next;
 	void *address;
 	size_t used;
-	struct cmd_queue_page *next;
 };
 
 #define CMD_QUEUE_PAGE_SIZE (1024 * 1024)
 static struct cmd_queue_page *cmd_queue_pages;
+static struct cmd_queue_page *cmd_queue_pages_tail;
 
 struct jtag_command *jtag_command_queue;
 static struct jtag_command **next_command_pointer = &jtag_command_queue;
@@ -100,8 +101,7 @@ void *cmd_queue_alloc(size_t size)
 	/* Done... */
 
 	if (*p_page) {
-		while ((*p_page)->next)
-			p_page = &((*p_page)->next);
+		p_page = &cmd_queue_pages_tail;
 		if (CMD_QUEUE_PAGE_SIZE - (*p_page)->used < size)
 			p_page = &((*p_page)->next);
 	}
@@ -113,6 +113,7 @@ void *cmd_queue_alloc(size_t size)
 					CMD_QUEUE_PAGE_SIZE : size;
 		(*p_page)->address = malloc(alloc_size);
 		(*p_page)->next = NULL;
+		cmd_queue_pages_tail = *p_page;
 	}
 
 	offset = (*p_page)->used;
@@ -134,6 +135,7 @@ static void cmd_queue_free(void)
 	}
 
 	cmd_queue_pages = NULL;
+	cmd_queue_pages_tail = NULL;
 }
 
 void jtag_command_queue_reset(void)