dpif-netdev: Add command to switch dpif implementation.

This commit adds a new command to allow the user to switch
the active DPIF implementation at runtime. A probe function
is executed before switching the DPIF implementation, to ensure
the CPU is capable of running the ISA required. For example, the
below code will switch to the AVX512 enabled DPIF assuming
that the runtime CPU is capable of running AVX512 instructions:

 $ ovs-appctl dpif-netdev/dpif-impl-set dpif_avx512

A new configuration flag is added to allow selection of the
default DPIF. This is useful for running the unit-tests against
the available DPIF implementations, without modifying each unit test.

The design of the testing & validation for ISA optimized DPIF
implementations is based around the work already upstream for DPCLS.
Note however that a DPCLS lookup has no state or side-effects, allowing
the auto-validator implementation to perform multiple lookups and
provide consistent statistic counters.

The DPIF component does have state, so running two implementations in
parallel and comparing output is not a valid testing method, as there
are changes in DPIF statistic counters (side effects). As a result, the
DPIF is tested directly against the unit-tests.

Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
Co-authored-by: Cian Ferriter <cian.ferriter@intel.com>
Signed-off-by: Cian Ferriter <cian.ferriter@intel.com>
Acked-by: Flavio Leitner <fbl@sysclose.org>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>

1 files changed, 34 insertions, 0 deletions

diff --git a/Documentation/topics/dpdk/bridge.rst b/Documentation/topics/dpdk/bridge.rst
index 526d5c959..06d1f943c 100644
--- a/Documentation/topics/dpdk/bridge.rst
+++ b/Documentation/topics/dpdk/bridge.rst
@@ -214,3 +214,37 @@ implementation ::
 
 Compile OVS in debug mode to have `ovs_assert` statements error out if
 there is a mis-match in the DPCLS lookup implementation.
+
+Datapath Interface Performance
+------------------------------
+
+The datapath interface (DPIF) or dp_netdev_input() is responsible for taking
+packets through the major components of the userspace datapath; such as
+miniflow_extract, EMC, SMC and DPCLS lookups, and a lot of the performance
+stats associated with the datapath.
+
+Just like with the SIMD DPCLS feature above, SIMD can be applied to the DPIF to
+improve performance.
+
+By default, dpif_scalar is used. The DPIF implementation can be selected by
+name ::
+
+    $ ovs-appctl dpif-netdev/dpif-impl-set dpif_avx512
+    DPIF implementation set to dpif_avx512.
+
+    $ ovs-appctl dpif-netdev/dpif-impl-set dpif_scalar
+    DPIF implementation set to dpif_scalar.
+
+Running Unit Tests with AVX512 DPIF
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Since the AVX512 DPIF is disabled by default, a compile time option is
+available in order to test it with the OVS unit test suite. When building with
+a CPU that supports AVX512, use the following configure option ::
+
+    $ ./configure --enable-dpif-default-avx512
+
+The following line should be seen in the configure output when the above option
+is used ::
+
+    checking whether DPIF AVX512 is default implementation... yes