Re: [PATCH 4/6] blk-mq: use EWMA to estimate congestion threshold

Jens Axboe
2017-07-11T18:25:16Z

On 07/11/2017 12:21 PM, Ming Lei wrote:
> When .queue_rq() returns BLK_STS_RESOURCE(BUSY), we can
> consider that there is congestion in either low level
> driver or hardware.
>
> This patch uses EWMA to estimate this congestion threshold,
> then this threshold can be used to detect/avoid congestion.

This whole patch set lacks some sort of reasoning why this
makes sense. I'm assuming you want to reduce unnecessary
restarts of the queue? I would much rather ensure that we only
start when we absolutely have to to begin with, I'm pretty sure
we have a number of cases where that is not so.

What happens with fluid congestion boundaries, with shared tags?

--
Jens Axboe