Re: [Cake] and the bad cpu news on arm is

[Jonathan Morton <chromatix99@gmail.com>]

> On 20 Dec, 2015, at 14:59, Dave Taht <dave.taht@gmail.com> wrote:
> 
> I do happen to like the set associativity idea, but it's proving
> really hard to show its value with any existing tests we have.

I’m sure we had those sorts of tests earlier on.  The 50:1 test might have been one of them.  Certainly, measuring Jain’s Fairness Index across the 50 flows should be revealing; with perfect flow isolation it should be close to unity, while with uncorrected hash collisions it should be noticeably inferior.

It’s certainly easy to detect when it’s avoiding hash collisions through the stats output, as that’s when the “indirect hit” counters start incrementing.

Perhaps when the next stage of flow isolation is actually in and working, the benefits will be easier to measure directly on a human scale.  I don’t think I’d be confident in my current approach to the problem unless the set-associative hash was in place.

 - Jonathan Morton