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

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Date: Fri, 14 Jun 2024 17:11:30 +0100
From: Simon Horman <horms@...nel.org>
To: Adrian Moreno <amorenoz@...hat.com>
Cc: netdev@...r.kernel.org, aconole@...hat.com, echaudro@...hat.com,
	i.maximets@....org, dev@...nvswitch.org,
	Yotam Gigi <yotam.gi@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2 4/9] net: psample: allow using rate as
 probability

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 <amorenoz@...hat.com>

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.

...