** 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 ** This series is an attempt to fix this situation by extending the existing psample infrastructure to carry a variable length user-defined cookie.
The main existing user of psample is tc's act_sample. It is also xtended to forward the action's cookie to psample.
Finally, OVS sample action is extended with a couple of attributes (OVS_SAMPLE_ATTR_PSAMPLE_{GROUP,COOKIE}) that contain a 32 group_id and a variable length cookie. When provided, OVS sends the packet to psample for observability.
In order to make it easier for users to receive samples coming from a specific source, group_id filtering is added to psample as well as a tracepoint for troubleshooting.
-- rfc_v2 -> v1: - Accomodate Ilya's comments. - Split OVS's attribute in two attributes and simplify internal handling of psample arguments. - Extend psample and tc with a user-defined cookie. - Add a tracepoint to psample to facilitate troubleshooting.
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 (8): net: netlink: export genl private pointer getters net: psample: add multicast filtering on group_id net: psample: add user cookie net: psample: add tracepoint net: sched: act_sample: add action cookie to sample net:openvswitch: add psample support selftests: openvswitch: add sample action. selftests: openvswitch: add psample test
Documentation/netlink/specs/ovs_flow.yaml | 6 + include/net/psample.h | 2 + include/uapi/linux/openvswitch.h | 49 ++++- include/uapi/linux/psample.h | 2 + net/netlink/genetlink.c | 2 + net/openvswitch/actions.c | 51 ++++- net/openvswitch/flow_netlink.c | 80 +++++-- net/psample/psample.c | 131 ++++++++++- net/psample/trace.h | 62 ++++++ net/sched/act_sample.c | 12 + .../selftests/net/openvswitch/openvswitch.sh | 97 +++++++- .../selftests/net/openvswitch/ovs-dpctl.py | 207 +++++++++++++++++- 12 files changed, 655 insertions(+), 46 deletions(-) create mode 100644 net/psample/trace.h