Re: [LSF/MM TOPIC] Two blk-mq related topics

[Jens Axboe <axboe@kernel.dk>]

On 1/29/18 4:46 PM, James Bottomley wrote:
> On Mon, 2018-01-29 at 14:00 -0700, Jens Axboe wrote:
>> On 1/29/18 1:56 PM, James Bottomley wrote:
>>>
>>> On Mon, 2018-01-29 at 23:46 +0800, Ming Lei wrote:
>>> [...]
>>>>
>>>> 2. When to enable SCSI_MQ at default again?
>>>
>>> I'm not sure there's much to discuss ... I think the basic answer
>>> is as soon as Christoph wants to try it again.
>>
>> FWIW, internally I've been running various IO intensive workloads on
>> what is essentially 4.12 upstream with scsi-mq the default (with
>> mq-deadline as the scheduler) and comparing IO workloads with a
>> previous 4.6 kernel (without scsi-mq), and things are looking
>> great.
>>
>> We're never going to iron out the last kinks with it being off
>> by default, I think we should attempt to flip the switch again
>> for 4.16.
> 
> Absolutely, I agree we turn it on ASAP.  I just don't want to be on the
> receiving end of Linus' flamethrower because a bug we already had
> reported against scsi-mq caused problems.  Get confirmation from the
> original reporters (or as close to it as you can) that their problems
> are fixed and we're good to go; he won't kick us nearly as hard for new
> bugs that turn up.

I agree, the functional issues definitely have to be verified to be
resolved. Various performance hitches we can dive into if they
crop up, but reintroducing some random suspend regression is not
acceptable.

-- 
Jens Axboe