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

From: Adrian Hunter <adrian.hunter@intel.com>
To: Jens Axboe <axboe@kernel.dk>, Linus Walleij <linus.walleij@linaro.org>
Cc: "linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Paolo Valente <paolo.valente@linaro.org>,
	Chunyan Zhang <zhang.chunyan@linaro.org>,
	Baolin Wang <baolin.wang@linaro.org>,
	linux-block@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
	Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH 06/16] mmc: core: replace waitqueue with worker
Date: Mon, 13 Mar 2017 11:25:37 +0200	[thread overview]
Message-ID: <e4b2c4bc-8627-2234-354d-c986f69b220f@intel.com> (raw)
In-Reply-To: <8f1f3d4c-410c-2632-c776-4ced363bdb0d@kernel.dk>

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?