Re: [PATCH 06/16] mmc: core: replace waitqueue with worker

Adrian Hunter
2017-03-13T09:25:37Z

On 11/03/17 00:05, Jens Axboe wrote:
> On 03/10/2017 07:21 AM, Adrian Hunter wrote:
>>> Essentially I take out that thread and replace it with this one worker
>>> introduced in this very patch. I agree the driver can block in many ways
>>> and that is why I need to have it running in process context, and this
>>> is what the worker introduced here provides.
>>
>> The last time I looked at the blk-mq I/O scheduler code, it pulled up to
>> qdepth requests from the I/O scheduler and left them on a local list while
>> running ->queue_rq(). That means blocking in ->queue_rq() leaves some
>> number of requests in limbo (not issued but also not in the I/O scheduler)
>> for that time.
>
> Look again, if we're not handling the requeued dispatches, we pull one
> at the time from the scheduler.
>

That's good :-)

Now the next thing ;-)

It looks like we either set BLK_MQ_F_BLOCKING and miss the possibility of
issuing synchronous requests immediately, or we don't set BLK_MQ_F_BLOCKING
in which case we are never allowed to sleep in ->queue_rq(). Is that true?