Re: [PATCH v2 0/2] ethdev: add random item support

[Stephen Hemminger <stephen@networkplumber.org>]

On Mon, 11 Sep 2023 18:55:45 +0200
Morten Brørup <mb@smartsharesystems.com> wrote:

> > From: Michael Baum [mailto:michaelba@nvidia.com]
> > Sent: Monday, 11 September 2023 08.42
> > 
> > Add support for matching random value using new
> > "rte_flow_item_random" structure.  
> 
> I get it. It can be used for things like stochastic sampling.
> 
> However, it doesn't provide support for e.g. 1/100 or 1/500.
> 
> So here's a suggestion:
> 
> Instead of "value" (which is irrelevant) & "mask" (which is what
> really controls the probability), wouldn't it be better if "value"
> was an inverse probability (and "mask" was irrelevant)? E.g.
> value=500 means that there is a 1 of 500 probability of a match.
> 
> Would this kind of random item better serve the purpose?
> 
> Or is the random item, in its current form, also required for other
> purposes?
> 

For netem (Linux kernel) needed to support expressing a percent in fixed
point number. The solution was to express it as:
    Percent = X / UINT32_MAX