On 08/30/2017 09:19 AM, Ming Lei wrote: > It is more reasonable to add requests to ->dispatch in way > of FIFO style, instead of LIFO style. > > Also in this way, we can allow to insert request at the front > of hw queue, which function is needed to fix one bug > in blk-mq's implementation of blk_execute_rq() > > Reported-by: Oleksandr Natalenko <[email protected]> > Tested-by: Oleksandr Natalenko <[email protected]> > Signed-off-by: Ming Lei <[email protected]> > --- > block/blk-mq-sched.c | 2 +- > block/blk-mq.c | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c > index 4ab69435708c..8d97df40fc28 100644 > --- a/block/blk-mq-sched.c > +++ b/block/blk-mq-sched.c > @@ -272,7 +272,7 @@ static bool blk_mq_sched_bypass_insert(struct > blk_mq_hw_ctx *hctx, > * the dispatch list. > */ > spin_lock(&hctx->lock); > - list_add(&rq->queuelist, &hctx->dispatch); > + list_add_tail(&rq->queuelist, &hctx->dispatch); > spin_unlock(&hctx->lock); > return true; > } > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 4603b115e234..fed3d0c16266 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -1067,7 +1067,7 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, > struct list_head *list) > blk_mq_put_driver_tag(rq); > > spin_lock(&hctx->lock); > - list_splice_init(list, &hctx->dispatch); > + list_splice_tail_init(list, &hctx->dispatch); > spin_unlock(&hctx->lock);
I'm not convinced this is safe, there's actually a reason why the request is added to the front and not the back. We do have reorder_tags_to_front() as a safe guard, but I'd much rather get rid of that than make this change. What's your reasoning here? Your changelog doesn't really explain why this fixes anything, it's very vague. -- Jens Axboe
