On Wed, 2017-09-06 at 15:34 +0800, weiping zhang wrote:
> On Tue, Sep 05, 2017 at 03:42:45PM +0000, Bart Van Assche wrote:
> > On Sun, 2017-09-03 at 21:46 +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/ioscheduler
> > > echo 1000000 > /sys/block/nvme0n1/queue/nr_requests
> > > cat /sys/block/nvme0n1/queue/nr_requests
> > > 1000000
> > >
> > > Signed-off-by: weiping zhang <zhangweiping@xxxxxxxxxxxxxxx>
> > > ---
> > > block/blk-mq.c | 7 +++++--
> > > 1 file changed, 5 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > > index f84d145..8303e5e 100644
> > > --- a/block/blk-mq.c
> > > +++ b/block/blk-mq.c
> > > @@ -2622,8 +2622,11 @@ 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),
> > > + if (nr > set->queue_depth) {
> > > + nr = set->queue_depth;
> > > + pr_warn("reduce nr_request to %u\n", nr);
> > > + }
> > > + ret = blk_mq_tag_update_depth(hctx, &hctx->tags, nr,
> > > false);
> > > } else {
> > > ret = blk_mq_tag_update_depth(hctx, &hctx->sched_tags,
> >
> > Shouldn't this code return -EINVAL or -ERANGE if 'nr' is too large? That will help to
> > keep user space code simple that updates the queue depth.
>
> Hi Bart,
>
> The reason why not return -EINVAL is keeping alin with minimum checking in queue_requests_store,
> if you insist return -EINVAL/-ERANGE, minimum checking should also keep
> same behavior. Both return error meesage and quietly changing are okey
> for me. Which way do you prefer ?
>
> static ssize_t
> 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;
>
> if (nr < BLKDEV_MIN_RQ)
> nr = BLKDEV_MIN_RQ;
Hello Jens,
Do you perhaps have a preference for one of the approaches that have been discussed
in this e-mail thread?
Thanks,
Bart.
