commit 7b5a3522 (loop: Limit the number of requests in the bio list) limit
the request number in loop queue to not over 128. Since the "request_fn" of
loop device is null, the requests number is not allowed tuned. Make it tunable
from sysfs can improve performance.
The following test is done on a machine with 512M memory. The backend of
/dev/loop1 is a nfs file.
[root@bijx mnt]# cat /sys/block/loop0/queue/nr_requests
128
[root@bijx mnt]# dd if=/dev/zero of=/dev/loop0 bs=1M count=5000
5000+0 records in
5000+0 records out
5242880000 bytes (5.2 GB) copied, 501.572 s, 10.5 MB/s
[root@bijx mnt]#
[root@bijx mnt]# echo 1024 > /sys/block/loop0/queue/nr_requests
[root@bijx mnt]# cat /sys/block/loop0/queue/nr_requests
1024
[root@bijx mnt]# dd if=/dev/zero of=/dev/loop0 bs=1M count=5000
5000+0 records in
5000+0 records out
5242880000 bytes (5.2 GB) copied, 464.481 s, 11.3 MB/s
Signed-off-by: Junxiao Bi <junxiao...@oracle.com>
---
block/blk-core.c | 6 ++++++
block/blk-sysfs.c | 9 +++------
2 files changed, 9 insertions(+), 6 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index 40d6548..58c4bd4 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -851,6 +851,12 @@ int blk_update_nr_requests(struct request_queue *q,
unsigned int nr)
q->nr_requests = nr;
blk_queue_congestion_threshold(q);
+ /* for loop device, return after set its nr_requests */
+ if (!q->request_fn) {
+ spin_unlock_irq(q->queue_lock);
+ return 0;
+ }
+
/* congestion isn't cgroup aware and follows root blkcg for now */
rl = &q->root_rl;
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 23321fb..c5456a5 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -51,9 +51,6 @@ queue_requests_store(struct request_queue *q, const char
*page, size_t count)
unsigned long nr;
int ret, err;
- if (!q->request_fn && !q->mq_ops)
- return -EINVAL;
-
ret = queue_var_store(&nr, page, count);
if (ret < 0)
return ret;
@@ -61,10 +58,10 @@ queue_requests_store(struct request_queue *q, const char
*page, size_t count)
if (nr < BLKDEV_MIN_RQ)
nr = BLKDEV_MIN_RQ;
- if (q->request_fn)
- err = blk_update_nr_requests(q, nr);
- else
+ if (q->mq_ops)
err = blk_mq_update_nr_requests(q, nr);
+ else
+ err = blk_update_nr_requests(q, nr);
if (err)
return err;
--
1.7.9.5
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