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

Jens Axboe
2017-01-12T04:44:22Z

On 01/11/2017 09:36 PM, Stephen Bates wrote:
>>>
>>> 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.
>>
>> --
>> Jens Axboe
>>
>
> I'd also be interested in this topic. Given that iopoll only really makes
> sense for low-latency, low queue depth environments (i.e. down below
> 10-20us) I'd like to discuss which drivers we think will need/want to be
> upgraded (aside from NVMe ;-)).
>
> I'd also be interested in discussing how best to enable and disable
> polling. In the past some of us have pushed for a "big hammer" to turn
> polling on for a given device or HW queue [1]. I'd like to discuss this
> again as well as looking at other methods above and beyond the preadv2
> system call and the HIPRI flag.

This is a separate topic. The initial proposal is for polling for
interrupt mitigation, you are talking about polling in the context of
polling for completion of an IO.

We can definitely talk about this form of polling as well, but it should
be a separate topic and probably proposed independently.

--
Jens Axboe