Re: [PATCH] bfq: do try insert merge before bfq_init_rq() call

[Yuwei Guan]

On 2022/10/14 22:50, Jan Kara wrote:
> On Thu 13-10-22 21:53:21, Yuwei Guan wrote:
> > It's useless to do bfq_init_rq(rq), if the rq can do merge first.
> >
> > In the patch 5f550ede5edf8, it moved to bfq_init_rq() before
> > blk_mq_sched_try_insert_merge(), but it's pointless,
> > as the fifo_time of next is not set yet,
> > and !list_empty(&next->queuelist) is 0, so it does not
> > need to reposition rq's fifo_time.
> >
> > And for the "hash lookup, try again" situation, as follow,
> > bfq_requests_merged() call can work normally.
> >
> > blk_mq_sched_try_insert_merge
> >    elv_attempt_insert_merge
> >      elv_rqhash_find
> >
> > Signed-off-by: Yuwei Guan <Yuwei.Guan@xxxxxxxxxxxxx>
> OK, after some thinking I agree. How much testing has this patch got?
> Because I'd like to verify we didn't overlook something.
>
> 							Honza
Thanks for reviewing.
I tested it with fio seq read case like bellow,
then check blk trace and bfq log.

[global]
name=fio-seq-reads
filename=fio-seq-reads
rw=read
bs=16K
direct=1
numjobs=4

[file1]
size=32m
ioengine=psync

What kinds of test cases you perfer to do, I will deal with them,
or we verify this patch together, if you have free time. :)
> > ---
> >   block/bfq-iosched.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> > index 7ea427817f7f..9845370a701c 100644
> > --- a/block/bfq-iosched.c
> > +++ b/block/bfq-iosched.c
> > @@ -6147,7 +6147,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
> >   		bfqg_stats_update_legacy_io(q, rq);
> >   #endif
> >   	spin_lock_irq(&bfqd->lock);
> > -	bfqq = bfq_init_rq(rq);
> > +
> >   	if (blk_mq_sched_try_insert_merge(q, rq, &free)) {
> >   		spin_unlock_irq(&bfqd->lock);
> >   		blk_mq_free_requests(&free);
> > @@ -6156,6 +6156,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
> >   
> >   	trace_block_rq_insert(rq);
> >   
> > +	bfqq = bfq_init_rq(rq);
> >   	if (!bfqq || at_head) {
> >   		if (at_head)
> >   			list_add(&rq->queuelist, &bfqd->dispatch);
> > --
> > 2.34.1