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: Jens Axboe <jaxboe@fusionio.com>

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: Jens Axboe <jaxboe@fusionio.com>
Jens Axboe
1 parent 841fdffdd3
Showing 3 changed files with 34 additions and 2 deletions Side-by-side Diff
block/blk-core.c
block/blk-sysfs.c
include/linux/blkdev.h
@@ -2111,7 +2111,8 @@
 	    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;
 }
@@ -250,6 +250,27 @@
 	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 @@
 	.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 @@
 	&queue_nomerges_entry.attr,
 	&queue_rq_affinity_entry.attr,
 	&queue_iostats_entry.attr,
+	&queue_random_entry.attr,
 	NULL,
 };
  
@@ -467,11 +467,13 @@
 #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 @@
 	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)
...	...	@@ -2111,7 +2111,8 @@
2111	2111	blk_update_request(rq->next_rq, error, bidi_bytes))
2112	2112	return true;
2113	2113
2114		- add_disk_randomness(rq->rq_disk);
	2114	+ if (blk_queue_add_random(rq->q))
	2115	+ add_disk_randomness(rq->rq_disk);
2115	2116
2116	2117	return false;
2117	2118	}
...	...	@@ -250,6 +250,27 @@
250	250	return ret;
251	251	}
252	252
	253	+static ssize_t queue_random_show(struct request_queue q, char page)
	254	+{
	255	+ return queue_var_show(blk_queue_add_random(q), page);
	256	+}
	257	+
	258	+static ssize_t queue_random_store(struct request_queue q, const char page,
	259	+ size_t count)
	260	+{
	261	+ unsigned long val;
	262	+ ssize_t ret = queue_var_store(&val, page, count);
	263	+
	264	+ spin_lock_irq(q->queue_lock);
	265	+ if (val)
	266	+ queue_flag_set(QUEUE_FLAG_ADD_RANDOM, q);
	267	+ else
	268	+ queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, q);
	269	+ spin_unlock_irq(q->queue_lock);
	270	+
	271	+ return ret;
	272	+}
	273	+
253	274	static ssize_t queue_iostats_show(struct request_queue q, char page)
254	275	{
255	276	return queue_var_show(blk_queue_io_stat(q), page);
...	...	@@ -374,6 +395,12 @@
374	395	.store = queue_iostats_store,
375	396	};
376	397
	398	+static struct queue_sysfs_entry queue_random_entry = {
	399	+ .attr = {.name = "add_random", .mode = S_IRUGO \| S_IWUSR },
	400	+ .show = queue_random_show,
	401	+ .store = queue_random_store,
	402	+};
	403	+
377	404	static struct attribute *default_attrs[] = {
378	405	&queue_requests_entry.attr,
379	406	&queue_ra_entry.attr,
...	...	@@ -394,6 +421,7 @@
394	421	&queue_nomerges_entry.attr,
395	422	&queue_rq_affinity_entry.attr,
396	423	&queue_iostats_entry.attr,
	424	+ &queue_random_entry.attr,
397	425	NULL,
398	426	};
399	427
...	...	@@ -467,11 +467,13 @@
467	467	#define QUEUE_FLAG_IO_STAT 15 /* do IO stats */
468	468	#define QUEUE_FLAG_DISCARD 16 /* supports DISCARD */
469	469	#define QUEUE_FLAG_NOXMERGES 17 /* No extended merges */
	470	+#define QUEUE_FLAG_ADD_RANDOM 18 /* Contributes to random pool */
470	471
471	472	#define QUEUE_FLAG_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) \| \
472	473	(1 << QUEUE_FLAG_CLUSTER) \| \
473	474	(1 << QUEUE_FLAG_STACKABLE) \| \
474		- (1 << QUEUE_FLAG_SAME_COMP))
	475	+ (1 << QUEUE_FLAG_SAME_COMP) \| \
	476	+ (1 << QUEUE_FLAG_ADD_RANDOM))
475	477
476	478	static inline int queue_is_locked(struct request_queue *q)
477	479	{
...	...	@@ -596,6 +598,7 @@
596	598	test_bit(QUEUE_FLAG_NOXMERGES, &(q)->queue_flags)
597	599	#define blk_queue_nonrot(q) test_bit(QUEUE_FLAG_NONROT, &(q)->queue_flags)
598	600	#define blk_queue_io_stat(q) test_bit(QUEUE_FLAG_IO_STAT, &(q)->queue_flags)
	601	+#define blk_queue_add_random(q) test_bit(QUEUE_FLAG_ADD_RANDOM, &(q)->queue_flags)
599	602	#define blk_queue_flushing(q) ((q)->ordseq)
600	603	#define blk_queue_stackable(q) \
601	604	test_bit(QUEUE_FLAG_STACKABLE, &(q)->queue_flags)