From e2e1a148bc45855816ae6b4692ce29d0020fa22e Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Wed, 9 Jun 2010 10:42:09 +0200 Subject: block: add sysfs knob for turning off disk entropy contributions There are two reasons for doing this: - On SSD disks, the completion times aren't as random as they are for rotational drives. So it's questionable whether they should contribute to the random pool in the first place. - Calling add_disk_randomness() has a lot of overhead. This adds /sys/block//queue/add_random that will allow you to switch off on a per-device basis. The default setting is on, so there should be no functional changes from this patch. Signed-off-by: Jens Axboe --- block/blk-core.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'block/blk-core.c') diff --git a/block/blk-core.c b/block/blk-core.c index f0640d7f800f..b4131d29148c 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -2111,7 +2111,8 @@ static bool blk_update_bidi_request(struct request *rq, int error, blk_update_request(rq->next_rq, error, bidi_bytes)) return true; - add_disk_randomness(rq->rq_disk); + if (blk_queue_add_random(rq->q)) + add_disk_randomness(rq->rq_disk); return false; } -- cgit v1.2.3