On Wed, Sep 06, 2017 at 01:00:44PM +0000, Bart Van Assche wrote:
> 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 <zhangweip...@didichuxing.com>
> > > > ---
> > > > 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.
Hello Jens,
Would you please give some comments about this patch,
Thanks
Weiping.
