linux-kernel - [PATCH 3/3] xen-blkfront: set queue paravirt flag

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Date:	Mon, 27 Oct 2008 18:45:54 +0900
From:	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	rusty@...tcorp.com.au, linux-kernel@...r.kernel.org,
	jeremy@...source.com
Subject: [PATCH 3/3] xen-blkfront: set queue paravirt flag

Xen's blkfront sets noop as the default I/O scheduler at initialization
time to avoid elevator overheads such as idling, but with the advent of
basic disk profiling capabilities this is not necessary anymore. We
should just tell the block layer that we are a paravirt front-end driver
and the elevator will automatically make the necessary adjustments.

Signed-off-by: Fernando Luis Vazquez Cao <fernando@....ntt.co.jp>
---

diff -urNp linux-2.6.28-rc2-orig/drivers/block/xen-blkfront.c linux-2.6.28-rc2/drivers/block/xen-blkfront.c
--- linux-2.6.28-rc2-orig/drivers/block/xen-blkfront.c	2008-10-27 17:41:53.000000000 +0900
+++ linux-2.6.28-rc2/drivers/block/xen-blkfront.c	2008-10-27 17:38:59.000000000 +0900
@@ -343,7 +343,7 @@ static int xlvbd_init_blk_queue(struct g
 	if (rq == NULL)
 		return -1;

-	elevator_init(rq, "noop");
+	queue_flag_set_unlocked(QUEUE_FLAG_VIRT, rq);

 	/* Hard sector size and max sectors impersonate the equiv. hardware. */
 	blk_queue_hardsect_size(rq, sector_size);

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