[linuxsh-dev] Too many requests are merged

[NIIBE Y. <gn...@m1...>]

GD-ROM driver is ready for new block device interface, but too many
request can be merged by default.  As it's very slow, it's better not
merge the requests.

	* drivers/cdrom/gdrom.c (gdrom_init): Let block device layer
	not merge the requests.

Index: drivers/cdrom/gdrom.c
===================================================================
RCS file: /cvsroot/linuxsh/kernel/drivers/cdrom/gdrom.c,v
retrieving revision 1.3
diff -u -r1.3 gdrom.c
--- drivers/cdrom/gdrom.c	2001/08/03 11:22:06	1.3
+++ drivers/cdrom/gdrom.c	2001/08/03 11:56:49
@@ -437,6 +437,22 @@
 	name:		"gdrom",
 };
 
+/*
+ * This driver works with new merge interface, but if the merge occurs
+ * performance gets really worse.  Hence, we disable the merge of requests.
+ */
+static int dont_merge_requests_fn(request_queue_t *q, struct request *req,
+				  struct request *next, int max_segments)
+{
+	return 0;
+}
+
+static int dont_bh_merge_fn(request_queue_t *q, struct request *req,
+                            struct buffer_head *bh, int max_segments)
+{
+	return 0;
+}
+
 static int __init gdrom_init(void)
 {
 	request_queue_t * q; 
@@ -455,6 +471,9 @@
 
 	q = BLK_DEFAULT_QUEUE(MAJOR_NR);
 	blk_init_queue(q, DEVICE_REQUEST);
+	q->back_merge_fn = dont_bh_merge_fn;
+	q->front_merge_fn = dont_bh_merge_fn;
+	q->merge_requests_fn = dont_merge_requests_fn;
 	blksize_size[MAJOR_NR] = &gdrom_blocksize;
 	hardsect_size[MAJOR_NR] = &gdrom_hardsecsize;
 	read_ahead[MAJOR_NR] = 4;
--