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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>
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parent
841fdffdd3
commit
e2e1a148bc
3 changed files with 34 additions and 2 deletions
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@ -2111,7 +2111,8 @@ static bool blk_update_bidi_request(struct request *rq, int error,
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blk_update_request(rq->next_rq, error, bidi_bytes))
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return true;
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add_disk_randomness(rq->rq_disk);
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if (blk_queue_add_random(rq->q))
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add_disk_randomness(rq->rq_disk);
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return false;
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}
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@ -250,6 +250,27 @@ queue_rq_affinity_store(struct request_queue *q, const char *page, size_t count)
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return ret;
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}
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static ssize_t queue_random_show(struct request_queue *q, char *page)
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{
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return queue_var_show(blk_queue_add_random(q), page);
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}
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static ssize_t queue_random_store(struct request_queue *q, const char *page,
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size_t count)
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{
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unsigned long val;
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ssize_t ret = queue_var_store(&val, page, count);
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spin_lock_irq(q->queue_lock);
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if (val)
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queue_flag_set(QUEUE_FLAG_ADD_RANDOM, q);
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else
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queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, q);
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spin_unlock_irq(q->queue_lock);
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return ret;
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}
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static ssize_t queue_iostats_show(struct request_queue *q, char *page)
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{
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return queue_var_show(blk_queue_io_stat(q), page);
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@ -374,6 +395,12 @@ static struct queue_sysfs_entry queue_iostats_entry = {
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.store = queue_iostats_store,
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};
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static struct queue_sysfs_entry queue_random_entry = {
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.attr = {.name = "add_random", .mode = S_IRUGO | S_IWUSR },
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.show = queue_random_show,
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.store = queue_random_store,
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};
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static struct attribute *default_attrs[] = {
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&queue_requests_entry.attr,
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&queue_ra_entry.attr,
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@ -394,6 +421,7 @@ static struct attribute *default_attrs[] = {
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&queue_nomerges_entry.attr,
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&queue_rq_affinity_entry.attr,
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&queue_iostats_entry.attr,
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&queue_random_entry.attr,
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NULL,
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};
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@ -467,11 +467,13 @@ struct request_queue
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#define QUEUE_FLAG_IO_STAT 15 /* do IO stats */
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#define QUEUE_FLAG_DISCARD 16 /* supports DISCARD */
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#define QUEUE_FLAG_NOXMERGES 17 /* No extended merges */
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#define QUEUE_FLAG_ADD_RANDOM 18 /* Contributes to random pool */
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#define QUEUE_FLAG_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \
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(1 << QUEUE_FLAG_CLUSTER) | \
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(1 << QUEUE_FLAG_STACKABLE) | \
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(1 << QUEUE_FLAG_SAME_COMP))
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(1 << QUEUE_FLAG_SAME_COMP) | \
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(1 << QUEUE_FLAG_ADD_RANDOM))
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static inline int queue_is_locked(struct request_queue *q)
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{
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@ -596,6 +598,7 @@ enum {
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test_bit(QUEUE_FLAG_NOXMERGES, &(q)->queue_flags)
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#define blk_queue_nonrot(q) test_bit(QUEUE_FLAG_NONROT, &(q)->queue_flags)
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#define blk_queue_io_stat(q) test_bit(QUEUE_FLAG_IO_STAT, &(q)->queue_flags)
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#define blk_queue_add_random(q) test_bit(QUEUE_FLAG_ADD_RANDOM, &(q)->queue_flags)
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#define blk_queue_flushing(q) ((q)->ordseq)
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#define blk_queue_stackable(q) \
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test_bit(QUEUE_FLAG_STACKABLE, &(q)->queue_flags)
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