linux-kernel - [PATCH] cfq: fix IOPRIO_CLASS

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Date:	Tue, 6 Nov 2007 23:05:10 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, Nick <gentuu@...il.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] cfq: fix IOPRIO_CLASS_IDLE delays

After the fresh boot:

	ionice -c3 -p $$
	echo cfq >> /sys/block/XXX/queue/scheduler
	dd if=/dev/XXX of=/dev/null bs=512 count=1

Now dd hangs in D state and the queue is completely stalled for approximately
INITIAL_JIFFIES + CFQ_IDLE_GRACE jiffies. This is because cfq_init_queue()
forgets to initialize cfq_data->last_end_request.

(I guess this patch is not complete, overflow is still possible)

Signed-off-by: Oleg Nesterov <oleg@...sign.ru>

--- cfq/block/cfq-iosched.c~	2007-08-09 19:59:26.000000000 +0400
+++ cfq/block/cfq-iosched.c	2007-11-06 22:39:08.000000000 +0300
@@ -2122,6 +2122,7 @@ static void *cfq_init_queue(struct reque
 
 	INIT_WORK(&cfqd->unplug_work, cfq_kick_queue);
 
+	cfqd->last_end_request = jiffies;
 	cfqd->cfq_quantum = cfq_quantum;
 	cfqd->cfq_fifo_expire[0] = cfq_fifo_expire[0];
 	cfqd->cfq_fifo_expire[1] = cfq_fifo_expire[1];

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