Re: [PATCH v13] blk-mq: Rework blk-mq timeout handling again

Jens Axboe
2018-05-22T17:17:06Z

On 5/22/18 10:44 AM, Jens Axboe wrote:
>
> On 5/22/18 10:25 AM, Bart Van Assche wrote:
>> Recently the blk-mq timeout handling code was reworked. See also Tejun
>> Heo, "[PATCHSET v4] blk-mq: reimplement timeout handling", 08 Jan 2018
>> (https://www.mail-archive.com/linux-block@vger.kernel.org/msg16985.html).
>> This patch reworks the blk-mq timeout handling code again. The timeout
>> handling code is simplified by introducing a state machine per request.
>> This change avoids that the blk-mq timeout handling code ignores
>> completions that occur after blk_mq_check_expired() has been called and
>> before blk_mq_rq_timed_out() has been called.
>
> I'll take a look at this again, getting rid of cmpxchg64 makes me
> much more comfortable.

FWIW, a quick pass on runtime testing works fine. As expected, it's
more efficient than what's currently in the kernel, testing with both
null_blk (1 and nr_cpus worth of queues), and nvme as well. A huge win
is that we shrink the request size from 360 bytes to 312, and I did
a small followup patch that brings that to 304. That's a 15% reduction,
massive.

--
Jens Axboe