[LSF/MM TOPIC][LSF/MM ATTEND] NAPI polling for block drivers

[Hannes Reinecke]

On 01/19/2017 11:57 AM, Ming Lei wrote:
> On Wed, Jan 11, 2017 at 11:07 PM, Jens Axboe <axboe at kernel.dk> wrote:
>> On 01/11/2017 06:43 AM, Johannes Thumshirn wrote:
>>> Hi all,
>>>
>>> I'd like to attend LSF/MM and would like to discuss polling for block drivers.
>>>
>>> Currently there is blk-iopoll but it is neither as widely used as NAPI in the
>>> networking field and accoring to Sagi's findings in [1] performance with
>>> polling is not on par with IRQ usage.
>>>
>>> On LSF/MM I'd like to whether it is desirable to have NAPI like polling in
>>> more block drivers and how to overcome the currently seen performance issues.
>>
>> It would be an interesting topic to discuss, as it is a shame that blk-iopoll
>> isn't used more widely.
> 
> I remembered that Keith and I discussed some issues of blk-iopoll:
> 
>     http://marc.info/?l=linux-block&m=147576999016407&w=2
> 
> seems which isn't addressed yet.
> 
That's a different poll.

For some obscure reasons you have a blk-mq-poll function (via
q->mq_ops->poll) and an irqpoll function.
The former is for polling completion of individual block-layer tags, the
latter for polling completions from the hardware instead of relying on
interrupts.

We're discussing the latter here, so that thread isn't really applicable
here. However, there have been requests to discuss the former at LSF/MM,
too. So there might be a chance of restarting that discussion.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
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