Message-ID: <f7d2a157-88d3-4f22-861d-8b926e71430a@ovn.org>
Date: Mon, 8 Apr 2024 15:16:03 +0200
From: Ilya Maximets <i.maximets@....org>
To: Adrian Moreno <amorenoz@...hat.com>, netdev@...r.kernel.org
Cc: i.maximets@....org, jiri@...nulli.us, xiyou.wangcong@...il.com,
 cmi@...dia.com, yotam.gi@...il.com, aconole@...hat.com, echaudro@...hat.com,
 horms@...nel.org
Subject: Re: [RFC net-next v2 0/5] net: openvswitch: Add sample multicasting.

On 4/8/24 14:57, Adrian Moreno wrote:
> ** Background **
> Currently, OVS supports several packet sampling mechanisms (sFlow,
> per-bridge IPFIX, per-flow IPFIX). These end up being translated into a
> userspace action that needs to be handled by ovs-vswitchd's handler
> threads only to be forwarded to some third party application that
> will somehow process the sample and provide observability on the
> datapath.
> 
> A particularly interesting use-case is controller-driven
> per-flow IPFIX sampling where the OpenFlow controller can add metadata
> to samples (via two 32bit integers) and this metadata is then available
> to the sample-collecting system for correlation.
> 
> ** Problem **
> The fact that sampled traffic share netlink sockets and handler thread
> time with upcalls, apart from being a performance bottleneck in the
> sample extraction itself, can severely compromise the datapath,
> yielding this solution unfit for highly loaded production systems.
> 
> Users are left with little options other than guessing what sampling
> rate will be OK for their traffic pattern and system load and dealing
> with the lost accuracy.
> 
> Looking at available infrastructure, an obvious candidated would be
> to use psample. However, it's current state does not help with the
> use-case at stake because sampled packets do not contain user-defined
> metadata.
> 
> ** Proposal **
> In this RFC_v2, I'd like to request feedback on an attempt to fix this
> situation by:
> 
> - Extending the existing psample infrastructure to carry a variable
> length user-defined cookie.
> - Extending the tc act_sample action to use the actions' cookie as
> psample metadata.
> - Extending the OVS sample action with an attribute
> (OVS_SAMPLE_ATTR_PSAMPLE) that contains a u32 group_id and a variable
> length cookie and use the the psample infrastructure to multicast
> the sample.
> - Extending psample to allow group_id filtering on listening sockets so
> that users can only receive samples they are interested in.
> 
> --
> rfc_v1 -> rfc_v2:
> - Use psample instead of a new OVS-only multicast group.
> - Extend psample and tc with a user-defined cookie.
> 
> 
> Adrian Moreno (5):
>   net: netlink: export genl private pointer getters
>   net: psample: add multicast filtering on group_id
>   net: psample: add user cookie
>   net:sched:act_sample: add action cookie to sample
>   net:openvswitch: add psample support
> 
>  include/net/psample.h            |   2 +
>  include/uapi/linux/openvswitch.h |  22 ++++-
>  include/uapi/linux/psample.h     |   2 +
>  net/netlink/genetlink.c          |   2 +
>  net/openvswitch/actions.c        |  52 ++++++++++--
>  net/openvswitch/datapath.c       |   2 +-
>  net/openvswitch/flow_netlink.c   |  78 +++++++++++++----
>  net/psample/psample.c            | 139 +++++++++++++++++++++++++++++--
>  net/sched/act_sample.c           |  12 +++
>  9 files changed, 277 insertions(+), 34 deletions(-)
> 

[copying my previous reply since this version actually has netdev@ in Cc]

Thanks, Adrian!

FWIW, I think this is a reasonable approach to the problem.

I won't do a full review since it's an RFC, but I'll leave some
comments for individual patches.

Best regards, Ilya Maximets.

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