Subject: Re: [PATCH net-next v2 4/9] net: psample: allow using rate as probability

From: Simon Horman <[email-masked]>
Date: Fri, 14 Jun 2024 17:11:30 +0100

On Mon, Jun 03, 2024 at 08:56:38PM +0200, Adrian Moreno wrote:
> Although not explicitly documented in the psample module itself, the
> definition of PSAMPLE_ATTR_SAMPLE_RATE seems inherited from act_sample.
> 
> Quoting tc-sample(8):
> "RATE of 100 will lead to an average of one sampled packet out of every
> 100 observed."
> 
> With this semantics, the rates that we can express with an unsigned
> 32-bits number are very unevenly distributed and concentrated towards
> "sampling few packets".
> For example, we can express a probability of 2.32E-8% but we
> cannot express anything between 100% and 50%.
> 
> For sampling applications that are capable of sampling a decent
> amount of packets, this sampling rate semantics is not very useful.
> 
> Add a new flag to the uAPI that indicates that the sampling rate is
> expressed in scaled probability, this is:
> - 0 is 0% probability, no packets get sampled.
> - U32_MAX is 100% probability, all packets get sampled.
> 
> Signed-off-by: Adrian Moreno <[email-masked]>

Hi Adrian,

Would it be possible to add appropriate documentation for
rate - both the original ratio variant, and the new probability
variant - somewhere?

That aside, this looks good to me.

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