Re: [PATCH] blk-mq: put the driver tag of nxt rq before first one is requeued

jianchao.wang
2017-09-13T01:01:25Z

Hi ming

On 09/12/2017 06:23 PM, Ming Lei wrote:
>> @@ -1029,14 +1029,20 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list)
>> if (list_empty(list))
>> bd.last = true;
>> else {
>> - struct request *nxt;
>> -
>> nxt = list_first_entry(list, struct request, queuelist);
>> bd.last = !blk_mq_get_driver_tag(nxt, NULL, false);
>> }
>>
>> ret = q->mq_ops->queue_rq(hctx, &bd);
>> if (ret == BLK_STS_RESOURCE) {
>> + /*
>> + * If an I/O scheduler has been configured and we got a
>> + * driver tag for the next request already, free it again.
>> + */
>> + if (!list_empty(list)) {
>> + nxt = list_first_entry(list, struct request, queuelist);
>> + blk_mq_put_driver_tag(nxt);
>> + }
> The following way might be more simple and clean:
>
> if (nxt)
> blk_mq_put_driver_tag(nxt);
>
> meantime 'nxt' need to be cleared inside the 'if (list_empty(list))'
> before .queue_rq().

I had ever thought about that, but to avoid add extra command in the
fast path, I made the patch above.

Thanks
Jianchao