[SCSI] iscsi: nodelay fix

From: tomof@acm.org

I'm not sure about this. I don't think that NODELAY option hurts
performance. However, open-iscsi does not use MSG_MORE properly with
sendpage, so NODELAY option hurts the open-iscsi performance.

I've attached a patch to fix NODELAY and MSG_MORE problems and the
write performance results with disktest.

I use Opteron boxes connected directly, Chelsio NICs, 1500-byte MTU,
64 KB I/O size, and the iSCSI parameters on open-iscsi web site.

With only NODELAY fix, the performance drops, as you said. On the
other hand, NODELAY and MSG_MORE fixes improve the performance
overall.
Signed-off-by: Alex Aizman <itn780@yahoo.com>
Signed-off-by: Dmitry Yusupov <dmitry_yus@yahoo.com>
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/iscsi_tcp.c

@@ -1385,7 +1385,7 @@ iscsi_sendpage(struct iscsi_conn *conn, struct iscsi_buf *buf,
 	BUG_ON(buf->sent + size > buf->sg.length);
 	if (size > *count)
 		size = *count;
-	if (buf->sent + size != buf->sg.length)
+	if (buf->sent + size != buf->sg.length || *count != size)
 		flags |= MSG_MORE;
 
 	res = iscsi_send(sk, buf, size, flags);