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

From: Tejun Heo
Date: Tue Oct 04 2016 - 12:28:06 EST


On Tue, Oct 04, 2016 at 06:22:28PM +0200, Paolo Valente wrote:
> Could you please elaborate more on this point? BFQ uses sectors
> served to measure service, and, on the all the fast devices on which
> we have tested it, it accurately distributes
> bandwidth as desired, redistributes excess bandwidth with any issue,
> and guarantees high responsiveness and low latency at application and
> system level (e.g., ~0 drop rate in video playback, with any background
> workload tested).

The same argument as before. Bandwidth is a very bad measure of IO
resources spent. For specific use cases (like desktop or whatever),
this can work but not generally.

> Could you please suggest me some test to show how sector-based
> guarantees fails?

Well, mix 4k random and sequential workloads and try to distribute the
acteual IO resources.