[Bug 1231] l3fwd: perf reports affected by silently enabling "fast free"

[Bug 1231] l3fwd: perf reports affected by silently enabling "fast free"

[bugzilla]

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https://bugs.dpdk.org/show_bug.cgi?id=1231

            Bug ID: 1231
           Summary: l3fwd: perf reports affected by silently enabling
                    "fast free"
           Product: DPDK
           Version: unspecified
          Hardware: All
                OS: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: examples
          Assignee: dev@dpdk.org
          Reporter: mb@smartsharesystems.com
  Target Milestone: ---

The l3fwd example application is used for benchmarking, including the official
NIC performance reports published on the DPDK web site [1].

A patch to silently enable the "fast free" (RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE)
optimization was applied to l3fwd [2][3] in January 2018.

This means that the performance reports starting from DPDK 18.02 do not reflect
generic performance, but the performance of applications that meet the
preconditions for using this optimization feature.

In order to prevent misleading performance results, such non-generic
optimizations should be not be silently enabled; they should be explicitly
enabled using a command line option in l3fwd.

The same applies to the coming "buffer recycle" optimization.

[1]: https://core.dpdk.org/perf-reports/
[2]: http://inbox.dpdk.org/dev/cover.1514280003.git.shahafs@mellanox.com/
[3]:
http://git.dpdk.org/dpdk/commit/examples/l3fwd/main.c?id=1ef9600b2d20078538ca4082f9a4adf2d9bd2ab2

PS: I don't oppose to NIC vendors publishing performance results using
non-generic optimizations such as "fast free" or the coming "buffer recycle",
but it should be fully disclosed which optimizations have been used to achieve
better results.

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