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Commit e2e1a148 authored by Jens Axboe's avatar Jens Axboe
Browse files

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/<dev>/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: default avatarJens Axboe <jaxboe@fusionio.com>
parent 841fdffd

block/blk-core.c

+2 −1
Original line number Diff line number Diff line
@@ -2111,6 +2111,7 @@ static bool blk_update_bidi_request(struct request *rq, int error, 
	    blk_update_request(rq->next_rq, error, bidi_bytes))

		return true;



	if (blk_queue_add_random(rq->q))

		add_disk_randomness(rq->rq_disk);



	return false;

block/blk-sysfs.c

+28 −0
Original line number Diff line number Diff line
@@ -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,

};

include/linux/blkdev.h

+4 −1
Original line number Diff line number Diff line
@@ -467,11 +467,13 @@ struct request_queue 
#define QUEUE_FLAG_IO_STAT     15	/* do IO stats */

#define QUEUE_FLAG_DISCARD     16	/* supports DISCARD */

#define QUEUE_FLAG_NOXMERGES   17	/* No extended merges */

#define QUEUE_FLAG_ADD_RANDOM  18	/* Contributes to random pool */



#define QUEUE_FLAG_DEFAULT	((1 << QUEUE_FLAG_IO_STAT) |		\

				 (1 << QUEUE_FLAG_CLUSTER) |		\

				 (1 << QUEUE_FLAG_STACKABLE)	|	\

				 (1 << QUEUE_FLAG_SAME_COMP))

				 (1 << QUEUE_FLAG_SAME_COMP)	|	\

				 (1 << QUEUE_FLAG_ADD_RANDOM))



static inline int queue_is_locked(struct request_queue *q)

{
@@ -596,6 +598,7 @@ enum { 
	test_bit(QUEUE_FLAG_NOXMERGES, &(q)->queue_flags)

#define blk_queue_nonrot(q)	test_bit(QUEUE_FLAG_NONROT, &(q)->queue_flags)

#define blk_queue_io_stat(q)	test_bit(QUEUE_FLAG_IO_STAT, &(q)->queue_flags)

#define blk_queue_add_random(q)	test_bit(QUEUE_FLAG_ADD_RANDOM, &(q)->queue_flags)

#define blk_queue_flushing(q)	((q)->ordseq)

#define blk_queue_stackable(q)	\

	test_bit(QUEUE_FLAG_STACKABLE, &(q)->queue_flags)