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Date:   Mon, 1 May 2023 06:34:44 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Bart Van Assche <bvanassche@acm.org>
Cc:     Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
        linux-block@vger.kernel.org, Jaegeuk Kim <jaegeuk@kernel.org>,
        Damien Le Moal <damien.lemoal@opensource.wdc.com>,
        Ming Lei <ming.lei@redhat.com>
Subject: Re: [PATCH v3 2/9] block: Micro-optimize
 blk_req_needs_zone_write_lock()
Message-ID: <20230501043444.GA19847@lst.de>
References: <20230424203329.2369688-1-bvanassche@acm.org> <20230424203329.2369688-3-bvanassche@acm.org> <20230428054446.GC8549@lst.de> <1c28f0b9-14f1-5fc1-4e15-52c4f6c2c91c@acm.org>
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On Fri, Apr 28, 2023 at 12:46:06PM -0700, Bart Van Assche wrote:
>>> +	if ((bio_op(bio) == REQ_OP_WRITE ||
>>> +	     bio_op(bio) == REQ_OP_WRITE_ZEROES) &&
>>> +	    disk_zone_is_seq(bio->bi_bdev->bd_disk, bio->bi_iter.bi_sector))
>>>   		return NULL;
>>
>> I find this a bit hard to hard to read.  Why not:
>>
>> 	if (disk_zone_is_seq(bio->bi_bdev->bd_disk, bio->bi_iter.bi_sector)) {
>> 	  	/*
>> 		 * Do not plug for writes that require zone locking.
>> 		 */
>> 		if (bio_op(bio) == REQ_OP_WRITE ||
>> 		    bio_op(bio) == REQ_OP_WRITE_ZEROES)
>> 			return NULL;
>> 	}
>
> In the above alternative the expensive check happens before a check that is not
> expensive at all. Do you really want me to call disk_zone_is_seq() before checking
> the operation type?

What expensive check?  The first check in disk_zone_is_seq is for
a zoned device, avoiding any further check if it is not.