[PATCH v4] blk-mq: fix nr_requests wrong value when modify it from sysfs

[PATCH v4] blk-mq: fix nr_requests wrong value when modify it from sysfs

[weiping zhang]

if blk-mq use "none" io scheduler, nr_request get a wrong value when
input a number > tag_set->queue_depth. blk_mq_tag_update_depth will get
the smaller one min(nr, set->queue_depth), and then q->nr_request get a
wrong value.

Reproduce:

echo none > /sys/block/nvme0n1/queue/scheduler
echo 1000000 > /sys/block/nvme0n1/queue/nr_requests
cat /sys/block/nvme0n1/queue/nr_requests
1000000

Signed-off-by: weiping zhang <zhangweiping@didichuxing.com>
---

Changes since v4:
 * fix typo in commit message(queue/ioscheduler => queue/scheduler)

Changes since v3:
 * remove compare nr with tags->qdepth, pass nr to blk_mq_tag_update_depth
directly

 * remove return EINVAL when user modify nr_request less than BLKDEV_MIN_RQ

Changes since v2:
 * add return EINVAL when user modify nr_request less than BLKDEV_MIN_RQ
 * remove pr_warn, and return EINVAL, if input number is too large

 block/blk-mq.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 98a1860..491e336 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2642,8 +2642,7 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
 		 * queue depth. This is similar to what the old code would do.
 		 */
 		if (!hctx->sched_tags) {
-			ret = blk_mq_tag_update_depth(hctx, &hctx->tags,
-							min(nr, set->queue_depth),
+			ret = blk_mq_tag_update_depth(hctx, &hctx->tags, nr,
 							false);
 		} else {
 			ret = blk_mq_tag_update_depth(hctx, &hctx->sched_tags,
-- 
2.9.4

Re: [PATCH v4] blk-mq: fix nr_requests wrong value when modify it from sysfs

[weiping zhang]

On Fri, Sep 22, 2017 at 11:36:28PM +0800, weiping zhang wrote:
> if blk-mq use "none" io scheduler, nr_request get a wrong value when
> input a number > tag_set->queue_depth. blk_mq_tag_update_depth will get
> the smaller one min(nr, set->queue_depth), and then q->nr_request get a
> wrong value.
> 
> Reproduce:
> 
> echo none > /sys/block/nvme0n1/queue/scheduler
> echo 1000000 > /sys/block/nvme0n1/queue/nr_requests
> cat /sys/block/nvme0n1/queue/nr_requests
> 1000000
> 
> Signed-off-by: weiping zhang <zhangweiping@didichuxing.com>
> ---
> 
> Changes since v4:
>  * fix typo in commit message(queue/ioscheduler => queue/scheduler)
> 
> Changes since v3:
>  * remove compare nr with tags->qdepth, pass nr to blk_mq_tag_update_depth
> directly
> 
>  * remove return EINVAL when user modify nr_request less than BLKDEV_MIN_RQ
> 
> Changes since v2:
>  * add return EINVAL when user modify nr_request less than BLKDEV_MIN_RQ
>  * remove pr_warn, and return EINVAL, if input number is too large
> 
>  block/blk-mq.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 98a1860..491e336 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2642,8 +2642,7 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
>  		 * queue depth. This is similar to what the old code would do.
>  		 */
>  		if (!hctx->sched_tags) {
> -			ret = blk_mq_tag_update_depth(hctx, &hctx->tags,
> -							min(nr, set->queue_depth),
> +			ret = blk_mq_tag_update_depth(hctx, &hctx->tags, nr,
>  							false);
>  		} else {
>  			ret = blk_mq_tag_update_depth(hctx, &hctx->sched_tags,
> -- 
> 2.9.4
> 

Hi Jens,

As you say before:
> blk_mq_tag_update_depth() should already return
> -EINVAL for the case where we can't grow the tags. Looks like this patch
> should simply remove the min(nr, set->queue_depth) and just pass in 'nr'.
I also find that hctx->tags->nr_tags equal to tag_set->queue_depth no matter use
hctx->sched_tags or not. So I think it's safe to verify 'nr' by
hctx->tags->nr_tags.

Thanks
weiping

Re: [PATCH v4] blk-mq: fix nr_requests wrong value when modify it from sysfs

[weiping zhang]

On Sat, Sep 30, 2017 at 10:57:31PM +0800, weiping zhang wrote:
> On Fri, Sep 22, 2017 at 11:36:28PM +0800, weiping zhang wrote:
> > if blk-mq use "none" io scheduler, nr_request get a wrong value when
> > input a number > tag_set->queue_depth. blk_mq_tag_update_depth will get
> > the smaller one min(nr, set->queue_depth), and then q->nr_request get a
> > wrong value.
> > 
> > Reproduce:
> > 
> > echo none > /sys/block/nvme0n1/queue/scheduler
> > echo 1000000 > /sys/block/nvme0n1/queue/nr_requests
> > cat /sys/block/nvme0n1/queue/nr_requests
> > 1000000
> > 
> > Signed-off-by: weiping zhang <zhangweiping@didichuxing.com>
> > ---
> > 
> > Changes since v4:
> >  * fix typo in commit message(queue/ioscheduler => queue/scheduler)
> > 
> > Changes since v3:
> >  * remove compare nr with tags->qdepth, pass nr to blk_mq_tag_update_depth
> > directly
> > 
> >  * remove return EINVAL when user modify nr_request less than BLKDEV_MIN_RQ
> > 
> > Changes since v2:
> >  * add return EINVAL when user modify nr_request less than BLKDEV_MIN_RQ
> >  * remove pr_warn, and return EINVAL, if input number is too large
> > 
> >  block/blk-mq.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index 98a1860..491e336 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -2642,8 +2642,7 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
> >  		 * queue depth. This is similar to what the old code would do.
> >  		 */
> >  		if (!hctx->sched_tags) {
> > -			ret = blk_mq_tag_update_depth(hctx, &hctx->tags,
> > -							min(nr, set->queue_depth),
> > +			ret = blk_mq_tag_update_depth(hctx, &hctx->tags, nr,
> >  							false);
> >  		} else {
> >  			ret = blk_mq_tag_update_depth(hctx, &hctx->sched_tags,
> > -- 
> > 2.9.4
> > 
> 
> Hi Jens,
> 
> As you say before:
> > blk_mq_tag_update_depth() should already return
> > -EINVAL for the case where we can't grow the tags. Looks like this patch
> > should simply remove the min(nr, set->queue_depth) and just pass in 'nr'.
> I also find that hctx->tags->nr_tags equal to tag_set->queue_depth no matter use
> hctx->sched_tags or not. So I think it's safe to verify 'nr' by
> hctx->tags->nr_tags.
> 
Hello Jens,

ping

Re: [PATCH v4] blk-mq: fix nr_requests wrong value when modify it from sysfs

[weiping zhang]

On Fri, Sep 22, 2017 at 11:36:28PM +0800, weiping zhang wrote:
> if blk-mq use "none" io scheduler, nr_request get a wrong value when
> input a number > tag_set->queue_depth. blk_mq_tag_update_depth will get
> the smaller one min(nr, set->queue_depth), and then q->nr_request get a
> wrong value.
> 
> Reproduce:
> 
> echo none > /sys/block/nvme0n1/queue/scheduler
> echo 1000000 > /sys/block/nvme0n1/queue/nr_requests
> cat /sys/block/nvme0n1/queue/nr_requests
> 1000000
> 
> Signed-off-by: weiping zhang <zhangweiping@didichuxing.com>
> ---
> 
> Changes since v4:
>  * fix typo in commit message(queue/ioscheduler => queue/scheduler)
> 
> Changes since v3:
>  * remove compare nr with tags->qdepth, pass nr to blk_mq_tag_update_depth
> directly
> 
>  * remove return EINVAL when user modify nr_request less than BLKDEV_MIN_RQ
> 
> Changes since v2:
>  * add return EINVAL when user modify nr_request less than BLKDEV_MIN_RQ
>  * remove pr_warn, and return EINVAL, if input number is too large
> 
>  block/blk-mq.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 98a1860..491e336 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2642,8 +2642,7 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
>  		 * queue depth. This is similar to what the old code would do.
>  		 */
>  		if (!hctx->sched_tags) {
> -			ret = blk_mq_tag_update_depth(hctx, &hctx->tags,
> -							min(nr, set->queue_depth),
> +			ret = blk_mq_tag_update_depth(hctx, &hctx->tags, nr,
>  							false);
>  		} else {
>  			ret = blk_mq_tag_update_depth(hctx, &hctx->sched_tags,
> -- 
> 2.9.4
> 
Hello Jens,

ping

Re: [PATCH v4] blk-mq: fix nr_requests wrong value when modify it from sysfs

[Jens Axboe]

On 09/22/2017 09:36 AM, weiping zhang wrote:
> if blk-mq use "none" io scheduler, nr_request get a wrong value when
> input a number > tag_set->queue_depth. blk_mq_tag_update_depth will get
> the smaller one min(nr, set->queue_depth), and then q->nr_request get a
> wrong value.
> 
> Reproduce:
> 
> echo none > /sys/block/nvme0n1/queue/scheduler
> echo 1000000 > /sys/block/nvme0n1/queue/nr_requests
> cat /sys/block/nvme0n1/queue/nr_requests
> 1000000

Sorry for the delay - looks good to me, and also tested that it does
fix the issue. Thanks, applied for 4.15.

-- 
Jens Axboe