RE: [patch net-next v2 5/8] Introduce sample tc action

-----Original Message-----
From: Simon Horman [mailto:simon.horman@netronome.com]
Sent: Wednesday, January 04, 2017 12:43 PM
To: Yotam Gigi <redacted>
Cc: Roopa Prabhu <redacted>; Jiri Pirko <jiri@resnulli.us>;
netdev@vger.kernel.org; davem@davemloft.net; Ido Schimmel
[off-list ref]; Elad Raz [off-list ref]; Nogah Frankel
[off-list ref]; Or Gerlitz [off-list ref];
jhs@mojatatu.com; geert+renesas@glider.be; stephen@networkplumber.org;
xiyou.wangcong@gmail.com; linux@roeck-us.net; john.fastabend@gmail.com
Subject: Re: [patch net-next v2 5/8] Introduce sample tc action

On Wed, Nov 16, 2016 at 04:26:44PM +0000, Yotam Gigi wrote:

quoted

quoted

-----Original Message-----
From: Roopa Prabhu [mailto:roopa@cumulusnetworks.com]
Sent: Wednesday, November 16, 2016 6:15 PM
To: Jiri Pirko <jiri@resnulli.us>
Cc: netdev@vger.kernel.org; davem@davemloft.net; Yotam Gigi
[off-list ref]; Ido Schimmel [off-list ref]; Elad Raz
[off-list ref]; Nogah Frankel [off-list ref]; Or Gerlitz
[off-list ref]; jhs@mojatatu.com; geert+renesas@glider.be;
stephen@networkplumber.org; xiyou.wangcong@gmail.com; linux@roeck-

us.net;

quoted

quoted

john.fastabend@gmail.com; simon.horman@netronome.com
Subject: Re: [patch net-next v2 5/8] Introduce sample tc action

On 11/14/16, 7:00 AM, Jiri Pirko wrote:

quoted

From: Yotam Gigi <redacted>

This action allow the user to sample traffic matched by tc classifier.
The sampling consists of choosing packets randomly, truncating them,
adding some informative metadata regarding the interface and the original
packet size and mark them with specific mark, to allow further tc rules to
match and process. The marked sample packets are then injected into the
device ingress qdisc using netif_receive_skb.

The packets metadata is packed using the ife encapsulation protocol, and
the outer packet's ethernet dest, source and eth_type, along with the
rate, mark and the optional truncation size can be configured from
userspace.

Example:
To sample ingress traffic from interface eth1, and redirect the sampled
the sampled packets to interface dummy0, one may use the commands:

tc qdisc add dev eth1 handle ffff: ingress

tc filter add dev eth1 parent ffff: \
	   matchall action sample rate 12 mark 17

Yotham, I am guessing in the future if one does not want to use mark,
the sample api is extensible to allow for other actions to be added.
This is from the general concern we had on using mark: some may not want to

use

quoted

quoted

mark.
As long as the api is extensible to allow an alternate way in the future,
we should be good. (We would prefer to not go down the path of having to
introduce
a new  'action sample' if this limits us in some way).

The code is extensible  - if one does want to add another action to sample, he
totally can :)

By the way, one of the reasons we removed the patches for now is that we
consider adding mirroring functionality to it instead of heaving two tc-rules.

Hi Yotham,

I see that this action combines several discrete sub-actions, some of which
duplicate functionality present in existing actions:

* sample
* truncate
* IFE encapsulation with metadata
* mark
* output (proposed)

I wonder if it would make sense to provided a mechanism whereby sampled
packets can be passed on to other actions. Something similar to the
existing pipe mechanism but allowing for the sampled and the original packets
to continue to be processed separately.

If so, it may be worth white-listing actions for which sampled packets are
known to work well to limit the scope for unforseen side effects.

Hi Simon,

The patches were removed and we intend to propose a different implementation for
that, using a dedicated sampling netlink channel, thus removing the need to
mark, mirror and IFE-pack the packets.

We intend to send in the next few weeks, so I guess you can comment on the new
version.

Thanks!