linux-kernel - Re: [PATCH V9 1/4] blk-mq: insert to hctx dispatch list when bypass

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Date:   Thu, 6 Dec 2018 09:12:02 +0800
From:   "jianchao.wang" <jianchao.w.wang@...cle.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     ming.lei@...hat.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V9 1/4] blk-mq: insert to hctx dispatch list when
 bypass_insert is true



On 12/6/18 12:25 AM, Jens Axboe wrote:
> On 12/5/18 12:43 AM, Jianchao Wang wrote:
>> We don't allow direct dispatch of anything but regular reads/writes
>> and insert all of non-read-write requests. However, this is not
>> correct for 'bypass_insert == true' case where inserting is ignored
>> and BLK_STS_RESOURCE is returned. The caller will fail forever.
>>
>> Fix it with inserting the non-read-write request to hctx dispatch
>> list to avoid to involve merge and io scheduler when bypass_insert
>> is true.
>>
>> Signed-off-by: Jianchao Wang <jianchao.w.wang@...cle.com>
>> ---
>>  block/blk-mq.c | 19 +++++++++++++++++--
>>  1 file changed, 17 insertions(+), 2 deletions(-)
>>
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index 9005505..153af90 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -1822,6 +1822,7 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
>>  {
>>  	struct request_queue *q = rq->q;
>>  	bool run_queue = true;
>> +	bool force = false;
>>  
>>  	/*
>>  	 * RCU or SRCU read lock is needed before checking quiesced flag.
>> @@ -1836,9 +1837,19 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
>>  		goto insert;
>>  	}
>>  
>> -	if (!blk_rq_can_direct_dispatch(rq) || (q->elevator && !bypass_insert))
>> +	if (q->elevator && !bypass_insert)
>>  		goto insert;
>>  
>> +	if (!blk_rq_can_direct_dispatch(rq)) {
>> +		/*
>> +		 * For 'bypass_insert == true' case, insert request into hctx
>> +		 * dispatch list.
>> +		 */
>> +		if (bypass_insert)
>> +			force = true;
>> +		goto insert;
>> +	}
> 
> Just do force = bypass_insert, no need for the if.
> 

Yes, I will do it.

Thanks
Jianchao