On 9/19/2014 6:38 PM, Jens Axboe wrote:
> On 09/19/2014 09:35 AM, Bart Van Assche wrote:
>> On 09/19/14 17:27, Ming Lei wrote:
>>> On Fri, Sep 19, 2014 at 11:21 PM, Bart Van Assche <bvanass...@acm.org>
>>> wrote:
>>>> On 09/19/14 16:28, Ming Lei wrote:
>>>>>
>>>>> On Fri, Sep 19, 2014 at 9:00 PM, Bart Van Assche <bvanass...@acm.org>
>>>>> wrote:
>>>>>>
>>>>>> @@ -2643,7 +2754,8 @@ static struct scsi_host_template srp_template = {
>>>>>> .proc_name = DRV_NAME,
>>>>>> .slave_configure = srp_slave_configure,
>>>>>> .info = srp_target_info,
>>>>>> - .queuecommand = srp_queuecommand,
>>>>>> + .queuecommand = srp_sq_queuecommand,
>>>>>> + .mq_queuecommand = srp_mq_queuecommand,
>>>>>
>>>>>
>>>>> Another choice is to obtain hctx from request directly, then mq can
>>>>> reuse the .queuecommand interface too.
>>>>
>>>>
>>>> Hello Ming,
>>>>
>>>> Is the hctx information already available in the request data structure ? I
>>>> have found a mq_ctx member but no hctx member. Did I perhaps overlook
>>>> something ?
>>>
>>> You are right, but the mq_ctx can be mapped to hctx like below way:
>>>
>>> ctx = rq->mq_ctx;
>>> hctx = q->mq_ops->map_queue(q, ctx->cpu);
>>
>> Hello Ming,
>>
>> Had you already noticed that the blk_mq_ctx data structure is a private
>> data structure (declared in block/blk-mq.h) and hence not available to
>> SCSI LLDs ? However, what might be possible is to cache the hctx pointer
>> in the request structure, e.g. like in the (completely untested) patch
>> below.
>
> ctx was meant to be private, unfortunately it's leaked a bit into other
> parts of block/. But it's still private within that, at least.
>
> Lets not add more stuff to struct request, it's already way too large.
> We could add an exported
>
> struct blk_mq_hw_ctx *blk_mq_request_to_hctx(struct request *rq)
> {
> struct request_queue *q = rq->q;
>
> return q->mq_ops->map_queue(q, rq->mq_ctx->cpu);
> }
>
> for this.
>
Hey,
So I agree that we shouldn't overload struct request with another
pointer, but it also seems a bit unnecessary to map again just to get
the hctx. Since in the future we would like LLDs to use scsi-mq why not
modify existing .queuecommand to pass hctx (or even better
hctx->driver_data) and for now LLDs won't use it. Once they choose to,
it will be available to them.
Sagi.
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