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Date:   Tue, 19 Oct 2021 23:25:44 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Pavel Begunkov <asml.silence@gmail.com>
Cc:     linux-block@vger.kernel.org, Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH 15/16] block: optimise blk_may_split for normal rw
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On Tue, Oct 19, 2021 at 10:24:24PM +0100, Pavel Begunkov wrote:
> +	unsigned int op = bio_op(bio);
> +
> +	if (op != REQ_OP_READ && op != REQ_OP_WRITE && op != REQ_OP_FLUSH) {
> +		switch (op) {
> +		case REQ_OP_DISCARD:
> +		case REQ_OP_SECURE_ERASE:
> +		case REQ_OP_WRITE_ZEROES:
> +		case REQ_OP_WRITE_SAME:
> +			return true; /* non-trivial splitting decisions */
> +		default:
> +			break;
> +		}

Nesting the if and the switch is too ugly to live.  If you want ifs do
just them.  But I'd really like to see numbers for this, also compared
to epxlicitly checking for REQ_OP_READ and REQ_OP_WRITE and maybe using
__builtin_expect for those values.