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Date:   Thu, 14 Oct 2021 08:32:32 +0100
From:   Christoph Hellwig <hch@infradead.org>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     linux-block@vger.kernel.org
Subject: Re: [PATCH 5/9] block: add support for blk_mq_end_request_batch()
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References: <20211013165416.985696-1-axboe@kernel.dk>
 <20211013165416.985696-6-axboe@kernel.dk>
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> +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?  

> +	/*
> +	 * 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.