[Bug 248652] netmap: pkt-gen TX huge pps difference between 11-STABLE and 12-STABLE/CURRENT on ix & ixl NIC

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=248652

--- Comment #1 from Vincenzo Maffione <vmaffione at FreeBSD.org> ---
Thanks for reporting.
What I can tell you for sure is that the difference is to be attributed to the
conversion of Intel drivers (em, ix, ixl) to iflib.
This impacted netmap because netmap support for iflib drivers (intel ones, vmx,
mgb, bnxt) is provided directly within the iflib core. IOW, no explicit netmap
code stays within the drivers.

I would say some physiological performance drop is to be expected, due to the
additional indirection introduced by iflib. However, the performance drop
should not be so large as reported in your experiments.
The 2.6 Mpps you get in the first comparison let me think that you may have
accidentally left ethernet flow control enabled, maybe?
Moreover, the last experiment is rather confusing, since you have actually a
performance improvement... this lets me think that maybe the configuration is
not 100% aligned between the two cases?

Have you tried to disable all the offloads? In 11-stable the driver-specific
netmap code does not program the offloads, whereas in CURRENT (and 12) the
iflib callbacks actually program the offloads also in case of netmap.

  # ifconfig ix0 -txcsum -rxcsum -tso4 -tso6 -lro -txcsum6 -rxcsum6

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