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>
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 306759b..58b53c3 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -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,
};