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

John Garry
2022-10-27T09:09:44Z

On 27/10/2022 02:16, Damien Le Moal wrote:
>> Signed-off-by: John Garry<john.garry@huawei.com>
>> ---
>> 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