linux-kernel - Re: [PATCH V9 3/4] blk-mq: issue directly with bypass 'false' in blk_mq_sched_insert

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Message-ID: <e25a0ba3-356a-35d9-e22b-63ba124f555a@kernel.dk>
Date:   Wed, 5 Dec 2018 19:13:03 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     "jianchao.wang" <jianchao.w.wang@...cle.com>
Cc:     ming.lei@...hat.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V9 3/4] blk-mq: issue directly with bypass 'false' in
 blk_mq_sched_insert_requests

On 12/5/18 6:11 PM, jianchao.wang wrote:
>> And why aren't we just using the list_empty() check like before, and not
>> having to add the inval cookie value?
> 
> Because we use 'bypass == false' here, so blk_mq_try_issue_directly
> will take over the request totally, so the request will always be
> removed from the list and finally, the list must be empty.
> 
> There is another way to identify the result of blk_mq_try_issue_directly.
> Currently,
> for the 'bypass == true' case,
>     it always return BLK_STS_OK,
> for the 'bypass == false' case,
>     it return the actual result, except for 'force == true' case
>     where the request has to be inserted into hctx dispatch list
>     and return a BLK_STS_OK.
> 
> We could let the 'bypass == true' case also return the actual result to
> show what has been done in the blk_mq_try_issue_directly and thus we could
> get the actual result of the last request.
> 
> Would you mind we handle it like this ?

I like that, sounds better than adding a new qc type.

-- 
Jens Axboe