linux-kernel - Re: [PATCH v8 13/13] nvmet-passthru: support block accounting

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Date:   Mon, 9 Sep 2019 13:32:56 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Sagi Grimberg <sagi@...mberg.me>, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Cc:     Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>,
        Stephen Bates <sbates@...thlin.com>, Jens Axboe <axboe@...com>,
        Keith Busch <kbusch@...nel.org>,
        Max Gurtovoy <maxg@...lanox.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v8 13/13] nvmet-passthru: support block accounting



On 2019-09-09 1:26 p.m., Sagi Grimberg wrote:
> 
>>>> Support block disk accounting by setting the RQF_IO_STAT flag
>>>> and gendisk in the request.
>>>>
>>>> After this change, IO counts will be reflected correctly in
>>>> /proc/diskstats for drives being used by passthru.
>>>>
>>>> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
>>>> ---
>>>>    drivers/nvme/target/io-cmd-passthru.c | 5 ++++-
>>>>    1 file changed, 4 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/nvme/target/io-cmd-passthru.c b/drivers/nvme/target/io-cmd-passthru.c
>>>> index 7557927a3451..63f12750a80d 100644
>>>> --- a/drivers/nvme/target/io-cmd-passthru.c
>>>> +++ b/drivers/nvme/target/io-cmd-passthru.c
>>>> @@ -410,6 +410,9 @@ static struct request *nvmet_passthru_blk_make_request(struct nvmet_req *req,
>>>>    	if (unlikely(IS_ERR(rq)))
>>>>    		return rq;
>>>>    
>>>> +	if (blk_queue_io_stat(q) && cmd->common.opcode != nvme_cmd_flush)
>>>> +		rq->rq_flags |= RQF_IO_STAT;
>>
>> Thanks for the review!
>>
>>> Does flush has data bytes in the request? Why the special casing?
>>
>> Well it was special cased in the vanilla blk account flow... But I think
>> it's required to be special cased so the IO and in_flight counts don't
>> count flushes (as they do not for regular block device traffic).
> 
> I think that the accounting exclude I/O that is yielded from the flush
> sequence. Don't think its relevant here...

What? Per blk_account_io_done(), RQF_FLUSH_SEQ will not be set by us for
passthru commands and I don't think it's appropriate to do so. Thus, if
we set RQF_IO_STAT for passthru flush commands, they will be counted
which we do not want.

Logan