Re: [PATCH RFC v3 01/22] blk-mq: Don't get budget for reserved requests

[John Garry]

On 27/10/2022 02:16, Damien Le Moal wrote:
> > Signed-off-by: John Garry<john.garry@xxxxxxxxxx>
> > ---
> >   block/blk-mq.c          | 4 +++-
> >   drivers/scsi/scsi_lib.c | 3 ++-
> >   2 files changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index 260adeb2e455..d8baabb32ea4 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -1955,11 +1955,13 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
> >   	errors = queued = 0;
> >   	do {
> >   		struct blk_mq_queue_data bd;
> > +		bool need_budget;
> >   
> >   		rq = list_first_entry(list, struct request, queuelist);
> >   
> >   		WARN_ON_ONCE(hctx != rq->mq_hctx);
> > -		prep = blk_mq_prep_dispatch_rq(rq, !nr_budgets);
> > +		need_budget = !nr_budgets && !blk_mq_is_reserved_rq(rq);
> > +		prep = blk_mq_prep_dispatch_rq(rq, need_budget);
> >   		if (prep != PREP_DISPATCH_OK)
> >   			break;
> Below this code, there is:
>
> 		if (nr_budgets)
> 			nr_budgets--;
>
> Don't you need to change that to:
>
> 		if (need_budget && nr_budgets)
> 			nr_budgets--;
>
> ? Otherwise, the accounting will be off.

Ah, yes, I think that you are right. I actually need to check nr_budgets 
usage further as nr_budgets initial value would be dependent on any 
reserved request requiring a budget (which we don't get).

Thanks,
John