On 10/14/21 1:32 AM, Christoph Hellwig wrote:
>> +void blk_mq_end_request_batch(struct io_batch *iob)
>> +{
>> + int tags[TAG_COMP_BATCH], nr_tags = 0, acct_tags = 0;
>> + struct blk_mq_hw_ctx *last_hctx = NULL;
>> + struct request *rq;
>> + u64 now = 0;
>> +
>> + while ((rq = rq_list_pop(&iob->req_list)) != NULL) {
>> + if (!now && blk_mq_need_time_stamp(rq))
>> + now = ktime_get_ns();
>> + blk_update_request(rq, rq->status, blk_rq_bytes(rq));
>> + __blk_mq_end_request_acct(rq, rq->status, now);
>> +
>> + if (rq->q->elevator) {
>> + blk_mq_free_request(rq);
>> + continue;
>> + }
>
> So why do we even bother adding requests with an elevator to the batch
> list?
You still get the benefit of amortized time keeping, and it's more
efficient to complete in batches rather than one-at-the-time. It's just
not as good as the non-elevator path.
>> + /*
>> + * csd is used for remote completions, fifo_time at scheduler time.
>> + * They are mutually exclusive. result is used at completion time
>> + * like csd, but for batched IO. Batched IO does not use IPI
>> + * completions.
>> + */
>> union {
>> struct __call_single_data csd;
>> u64 fifo_time;
>> + blk_status_t status;
>> };
>
> The ->status field isn't needed any more now that error completions
> aren't batched.
Killed.
--
Jens Axboe
