netdev - Re: [PATCH] filter: added BPF random opcode

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Date:	Wed, 16 Apr 2014 18:38:16 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	Chema Gonzalez <chema@...gle.com>,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Daniel Borkmann <dborkman@...hat.com>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH] filter: added BPF random opcode

On Tue, 2014-04-15 at 23:24 -0700, Alexei Starovoitov wrote:

> In particular I don't find the reason of moving random
> packet sampling into kernel to be that great.
> pcap cannot receive them quickly enough anyway,
> so there are drops already.
> Just randomly pick packets that reached the user space.
> Why add this to the kernel? I don't see how it can improve accuracy.

It has nothing to do with speed or accuracy.

Being able to intercept 0.001 % of the packets (and not 0.001 % of the
flows...) can be useful to network operators.

_Then_ if its super super super fast, thats better, of course.

Suggesting to intercept all packets, then filtering 99.999 % of them in
user space is not going to work. Its going to be super super super slow.



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