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

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Date: Mon, 17 Jun 2024 06:32:14 +0000
From: Adrián Moreno <amorenoz@...hat.com>
To: Simon Horman <horms@...nel.org>
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 Fri, Jun 14, 2024 at 05:11:30PM GMT, Simon Horman wrote:
> 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?
>

Hi Simon, thanks for the suggestion. Would the uapi header be a good
place for such documentation?

> That aside, this looks good to me.
>
> ...
>