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From: Logan Gunthorpe <logang@deltatee.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@fb.com>, Sagi Grimberg <sagi@grimberg.me>,
	Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>,
	linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
	Stephen Bates <sbates@raithlin.com>,
	linux-block@vger.kernel.org, Keith Busch <kbusch@kernel.org>,
	linux-fsdevel@vger.kernel.org, Max Gurtovoy <maxg@mellanox.com>
Subject: Re: [PATCH v9 10/12] block: don't check blk_rq_is_passthrough() in blk_do_io_stat()
Date: Thu, 10 Oct 2019 11:56:48 -0600
Message-ID: <d0b7e064-2e28-83b0-1593-405ab75d5bd2@deltatee.com> (raw)
In-Reply-To: <20191010100526.GA27209@lst.de>

Hey,

Thanks for the thorough review, lots here to go through. I'll address it
all as I have time and try to get the prep work done first, as soon as I
can.

On 2019-10-10 4:05 a.m., Christoph Hellwig wrote:
>> @@ -319,7 +319,7 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
>>  	rq->cmd_flags = op;
>>  	if (data->flags & BLK_MQ_REQ_PREEMPT)
>>  		rq->rq_flags |= RQF_PREEMPT;
>> -	if (blk_queue_io_stat(data->q))
>> +	if (blk_queue_io_stat(data->q) && !blk_rq_is_passthrough(rq))
>>  		rq->rq_flags |= RQF_IO_STAT;
> 
> This needs a comment why we don't account passthrough requests by
> default.  And I'm really curious about the answer, because I don't
> know it myself.

Yes, sadly, I don't know this answer either but the comment made it
appear that someone did it deliberately. Digging into git blame suggests
that it just evolved that way. The check was originally added in 2005
here with blk_fs_request():

commit d72d904a5367 ("[BLOCK] Update read/write block io statistics at
completion time")

blk_fs_request() evolved to become blk_rq_is_passthrough() but I suspect
no one ever considered whether we want to account the passthru requests.

So, I'll leave this restriction out and see if anyone complains.

Logan

>>   *	a) it's attached to a gendisk, and
>>   *	b) the queue had IO stats enabled when this request was started, and
>> - *	c) it's a file system request
>> + *	c) it's a file system request (RQF_IO_STAT will not be set otherwise)
> 
> c) should just go away now based on your changes.
> 
>>  static inline bool blk_do_io_stat(struct request *rq)
>>  {
>>  	return rq->rq_disk &&
>> -	       (rq->rq_flags & RQF_IO_STAT) &&
>> -		!blk_rq_is_passthrough(rq);
>> +	       (rq->rq_flags & RQF_IO_STAT);
> 
> The check can be collapsed onto a single line now.
> 



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Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-09 19:25 [PATCH v9 00/12] nvmet: add target passthru commands support Logan Gunthorpe
2019-10-09 19:25 ` [PATCH v9 01/12] nvme-core: introduce nvme_ctrl_get_by_path() Logan Gunthorpe
2019-10-09 22:13   ` Keith Busch
2019-10-10 11:37   ` Christoph Hellwig
2019-10-09 19:25 ` [PATCH v9 02/12] nvme-core: export existing ctrl and ns interfaces Logan Gunthorpe
2019-10-09 22:14   ` Keith Busch
2019-10-09 19:25 ` [PATCH v9 03/12] nvmet: add return value to nvmet_add_async_event() Logan Gunthorpe
2019-10-09 22:17   ` Keith Busch
2019-10-09 19:25 ` [PATCH v9 04/12] nvmet: make nvmet_copy_ns_identifier() non-static Logan Gunthorpe
2019-10-09 22:18   ` Keith Busch
2019-10-10 11:50   ` Christoph Hellwig
2019-10-09 19:25 ` [PATCH v9 05/12] Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com> [logang@deltatee.com: fixed some of the wording in the help message] Signed-off-by: Logan Gunthorpe <logang@deltatee.com> Reviewed-by: Max Gurtovoy <maxg@mellanox.com> Logan Gunthorpe
2019-10-10 12:34   ` Christoph Hellwig
2019-10-09 19:25 ` [PATCH v9 05/12] nvmet-passthru: add passthru code to process commands Logan Gunthorpe
2019-10-09 19:25 ` [PATCH v9 06/12] nvmet-passthru: add enable/disable helpers Logan Gunthorpe
2019-10-09 19:25 ` [PATCH v9 07/12] nvmet-core: don't check the data len for pt-ctrl Logan Gunthorpe
2019-10-10 11:04   ` Christoph Hellwig
2019-10-09 19:25 ` [PATCH v9 08/12] nvmet-tcp: don't check data_len in nvmet_tcp_map_data() Logan Gunthorpe
2019-10-10 11:07   ` Christoph Hellwig
2019-10-09 19:25 ` [PATCH v9 09/12] nvmet-configfs: introduce passthru configfs interface Logan Gunthorpe
2019-10-09 19:25 ` [PATCH v9 10/12] block: don't check blk_rq_is_passthrough() in blk_do_io_stat() Logan Gunthorpe
2019-10-10 10:05   ` Christoph Hellwig
2019-10-10 17:56     ` Logan Gunthorpe [this message]
2019-10-09 19:25 ` [PATCH v9 11/12] block: call blk_account_io_start() in blk_execute_rq_nowait() Logan Gunthorpe
2019-10-10 10:06   ` Christoph Hellwig
2019-10-09 19:25 ` [PATCH v9 12/12] nvmet-passthru: support block accounting Logan Gunthorpe

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