During normal operations, it is useful to understand when a particular flow
gets removed from the system. This can be useful when debugging performance
issues tied to ofproto flow changes, trying to determine deployed traffic
patterns, or while debugging dynamic systems where ports come and go.
Prior to this change, there was a lack of visibility around flow expiration.
The existing debugging infrastructure could tell us when a flow was added to
the datapath, but not when it was removed or why.
This change introduces a USDT probe at the point where the revalidator
determines that the flow should be removed. Additionally, we track the
reason for the flow eviction and provide that information as well. With
this change, we can track the complete flow lifecycle for the netlink
datapath by hooking the upcall tracepoint in kernel, the flow put USDT, and
the revalidator USDT, letting us watch as flows are added and removed from
the kernel datapath.
This change only enables this information via USDT probe, so it won't be
possible to access this information any other way (see:
Documentation/topics/usdt-probes.rst).
Also included is a script (utilities/usdt-scripts/flow_reval_monitor.py)
which serves as a demonstration of how the new USDT probe might be used
going forward.
Co-authored-by: Aaron Conole <aconole@redhat.com>
Acked-by: Han Zhou <hzhou@ovn.org>
Signed-off-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: Kevin Sprague <ksprague0711@gmail.com>
Signed-off-by: Eelco Chaudron <echaudro@redhat.com>
