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 ++- block/blk-sysfs.c | 28 ++++++++++++++++++++++++++++ 2 files changed, 30 insertions(+), 1 deletion(-) (limited to 'block') 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; } diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 306759bbdf1b..58b53c354c2c 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -250,6 +250,27 @@ queue_rq_affinity_store(struct request_queue *q, const char *page, size_t count) return ret; } +static ssize_t queue_random_show(struct request_queue *q, char *page) +{ + return queue_var_show(blk_queue_add_random(q), page); +} + +static ssize_t queue_random_store(struct request_queue *q, const char *page, + size_t count) +{ + unsigned long val; + ssize_t ret = queue_var_store(&val, page, count); + + spin_lock_irq(q->queue_lock); + if (val) + queue_flag_set(QUEUE_FLAG_ADD_RANDOM, q); + else + queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, q); + spin_unlock_irq(q->queue_lock); + + return ret; +} + static ssize_t queue_iostats_show(struct request_queue *q, char *page) { return queue_var_show(blk_queue_io_stat(q), page); @@ -374,6 +395,12 @@ static struct queue_sysfs_entry queue_iostats_entry = { .store = queue_iostats_store, }; +static struct queue_sysfs_entry queue_random_entry = { + .attr = {.name = "add_random", .mode = S_IRUGO | S_IWUSR }, + .show = queue_random_show, + .store = queue_random_store, +}; + static struct attribute *default_attrs[] = { &queue_requests_entry.attr, &queue_ra_entry.attr, @@ -394,6 +421,7 @@ static struct attribute *default_attrs[] = { &queue_nomerges_entry.attr, &queue_rq_affinity_entry.attr, &queue_iostats_entry.attr, + &queue_random_entry.attr, NULL, }; -- cgit v1.2.2