[Bloat] an observation from the field

[David Collier-Brown]

On 2018-08-28 1:07 p.m., Dave Taht wrote:
> In looking over the increasingly vast sqm-related deployment, there's
> a persistent data point that pops up regarding inbound shaping at high
> rates.
>
> We give users a choice - run out of cpu at those rates or do inbound
> sqm at a rate their cpu can afford.  A remarkable percentage are
> willing to give up tons of bandwidth in order to avoid latency
> excursions (oft measured, even in these higher speed 200+Mbit
> deployments, in the 100s of ms) -

Humans experience delays directly, and so perceive systems with high 
latency as "slow". The proverbial "man on the Clapham omnibus" therefor 
responds to high-latency systems with disgust.

A trained scientist, however, runs the risk of choosing something that 
requires complicated measurement schemes, and might well choose to 
optimize for throughput, as that sounds like a desirable measure, one 
matching their intuitions of what "fast" means.

Alas, in this case the scientist's intuition is far poorer than the 
random person's direct experience.

> At least some users want low delay always. It's just the theorists
> that want high utilization right at the edge of capacity. Users are
> forgiving about running out of cpu - disgruntled, but forgiving.
>
> Certainly I'm back at the point of recommending tbf+fq_codel for
> inbound shaping at higher rates - and looking at restoring the high
> speed version of cake - and I keep thinking a better policer is
> feasible.
>
My advice to engineers? First, go for things you can both experience and 
measure, and only then things you have to measure.

--dave

-- 
David Collier-Brown,         | Always do right. This will gratify
System Programmer and Author | some people and astonish the rest
davecb at spamcop.net           |                      -- Mark Twain