Re: [PATCH V3 00/11] block-throttle: add .high limit

From: Vivek Goyal
Date: Thu Oct 06 2016 - 13:49:58 EST

On Thu, Oct 06, 2016 at 03:15:50PM +0200, Paolo Valente wrote:

> Shaohua, I have just realized that I have unconsciously defended a
> wrong argument. Although all the facts that I have reported are
> evidently true, I have argued as if the question was: "do we need to
> throw away throttling because there is proportional, or do we need to
> throw away proportional share because there is throttling?". This
> question is simply wrong, as I think consciously (sorry for my
> dissociated behavior :) ).

I was wondering about the same. We need both and both should be able
to work with fast devices of today using blk-mq interfaces without
much overhead.

> The best goal to achieve is to have both a good throttling mechanism,
> and a good proportional share scheduler. This goal would be valid if
> even if there was just one important scenario for each of the two
> approaches. The vulnus here is that you guys are constantly, and
> rightly, working on solutions to achieve and consolidate reasonable
> QoS guarantees, but an apparently very good proportional-share
> scheduler has been kept off for years. If you (or others) have good
> arguments to support this state of affairs, then this would probably
> be an important point to discuss.

Paolo, CFQ is legacy now and if we can come up with a proportional
IO mechanism which works reasonably well with fast devices using
blk-mq interfaces, that will be much more interesting.