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