[PATCH linux-2.6.12-rc6-mm1] blk: elevator unplug thresh hanlding fix

[Tejun Heo]

 Hello, Jens.
 Hello, Andrew.

 This patch fixes q->unplug_thresh condition check in
__elv_add_request().  rq.count[READ] + rq.count[WRITE] can increase
more than one if another thread has allocated a request after the
current request is allocated or in_flight could have changed resulting
in larger-than-one change of nrq, thus breaking the threshold
mechanism.

 Signed-off-by: Tejun Heo <htejun@xxxxxxxxx>

Index: blk-fixes/drivers/block/elevator.c
===================================================================
--- blk-fixes.orig/drivers/block/elevator.c	2005-06-16 12:16:59.000000000 +0900
+++ blk-fixes/drivers/block/elevator.c	2005-06-16 12:17:03.000000000 +0900
@@ -352,7 +352,7 @@ void __elv_add_request(request_queue_t *
 			int nrq = q->rq.count[READ] + q->rq.count[WRITE]
 				  - q->in_flight;
 
-			if (nrq == q->unplug_thresh)
+			if (nrq >= q->unplug_thresh)
 				__generic_unplug_device(q);
 		}
 	} else

-
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