From: Jens Axboe <axboe@kernel.dk>
To: Bart Van Assche <bvanassche@acm.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Cc: Mike Snitzer <snitzer@redhat.com>, Ming Lei <ming.lei@redhat.com>
Subject: Re: [PATCH v3] blk-mq: punt failed direct issue to dispatch list
Date: Fri, 7 Dec 2018 09:24:53 -0700 [thread overview]
Message-ID: <693ac87a-ebb5-2e4e-25e5-92a1d3865c8f@kernel.dk> (raw)
In-Reply-To: <1544199585.185366.303.camel@acm.org>
On 12/7/18 9:19 AM, Bart Van Assche wrote:
> On Thu, 2018-12-06 at 22:17 -0700, Jens Axboe wrote:
>> Instead of making special cases for what we can direct issue, and now
>> having to deal with DM solving the livelock while still retaining a BUSY
>> condition feedback loop, always just add a request that has been through
>> ->queue_rq() to the hardware queue dispatch list. These are safe to use
>> as no merging can take place there. Additionally, if requests do have
>> prepped data from drivers, we aren't dependent on them not sharing space
>> in the request structure to safely add them to the IO scheduler lists.
>
> How about making blk_mq_sched_insert_request() complain if a request is passed
> to it in which the RQF_DONTPREP flag has been set to avoid that this problem is
> reintroduced in the future? Otherwise this patch looks fine to me.
I agree, but I think we should do that as a follow up patch. I don't want to
touch this one if we can avoid it. The thought did cross my mind, too. It
should be impossible now that everything goes to the dispatch list.
--
Jens Axboe
next prev parent reply other threads:[~2018-12-07 16:24 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-07 5:17 [PATCH v3] blk-mq: punt failed direct issue to dispatch list Jens Axboe
2018-12-07 8:24 ` Ming Lei
2018-12-07 10:50 ` Ming Lei
2018-12-07 15:15 ` Mike Snitzer
2018-12-07 16:19 ` Bart Van Assche
2018-12-07 16:24 ` Jens Axboe [this message]
2018-12-07 16:35 ` Jens Axboe
2018-12-07 16:41 ` Bart Van Assche
2018-12-07 16:45 ` Jens Axboe
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