From: Jeff Moyer <jmoyer@redhat.com>
Date: Tue, 15 Dec 2009 13:08:36 -0500
Subject: [block] iosched: reset batch for ordered requests
Message-id: <1260882517-14489-2-git-send-email-jmoyer@redhat.com>
Patchwork-id: 21950
O-Subject: [RHEL5 PATCH 1/2] Deadline iosched: Reset batch for ordered requests
Bugzilla: 462472
RH-Acked-by: Vivek Goyal <vgoyal@redhat.com>

fixes bug 462472

commit dfb3d72a9aa519672c9ae06f0d2f93eccb35482f
Author: Aaron Carroll <aaronc@gelato.unsw.edu.au>
Date:   Tue Oct 30 10:40:13 2007 +0100

    Deadline iosched: Reset batch for ordered requests

    The deadline I/O scheduler does not reset the batch count when starting
    a new batch at a higher-sectored request.  This means the second and
    subsequent batch in the same data direction will never exceed a single
    request in size whenever higher-sectored requests are pending.

    This patch gives new batches in the same data direction as old ones
    their full quota of requests by resetting the batch count.

    Signed-off-by: Aaron Carroll <aaronc@gelato.unsw.edu.au>
    Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>

diff --git a/block/deadline-iosched.c b/block/deadline-iosched.c
index c7ca9f0..fcf0482 100644
--- a/block/deadline-iosched.c
+++ b/block/deadline-iosched.c
@@ -522,12 +522,11 @@ dispatch_writes:
 dispatch_find_request:
 	/*
 	 * we are not running a batch, find best request for selected data_dir
+	 * and start a new batch
 	 */
 	if (deadline_check_fifo(dd, data_dir)) {
 		/* An expired request exists - satisfy it */
-		dd->batching = 0;
 		drq = list_entry_fifo(dd->fifo_list[data_dir].next);
-		
 	} else if (dd->next_drq[data_dir]) {
 		/*
 		 * The last req was the same dir and we have a next request in
@@ -540,10 +539,11 @@ dispatch_find_request:
 		 * higher-sectored requests. Go back to the lowest sectored
 		 * request (1 way elevator) and start a new batch.
 		 */
-		dd->batching = 0;
 		drq = deadline_find_first_drq(dd, data_dir);
 	}
 
+	dd->batching = 0;
+
 dispatch_request:
 	/*
 	 * drq is the selected appropriate request.