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>

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

acinclude.m4

@@ -30,6 +30,21 @@ AC_DEFUN([OVS_CHECK_DPCLS_AUTOVALIDATOR], [
   fi
 ])
 
+dnl Set OVS DPIF default implementation at configure time for running the unit
+dnl tests on the whole codebase without modifying tests per DPIF impl
+AC_DEFUN([OVS_CHECK_DPIF_AVX512_DEFAULT], [
+  AC_ARG_ENABLE([dpif-default-avx512],
+                [AC_HELP_STRING([--enable-dpif-default-avx512], [Enable DPIF AVX512 implementation as default.])],
+                [dpifavx512=yes],[dpifavx512=no])
+  AC_MSG_CHECKING([whether DPIF AVX512 is default implementation])
+  if test "$dpifavx512" != yes; then
+    AC_MSG_RESULT([no])
+  else
+    OVS_CFLAGS="$OVS_CFLAGS -DDPIF_AVX512_DEFAULT"
+    AC_MSG_RESULT([yes])
+  fi
+])
+
 dnl OVS_ENABLE_WERROR
 AC_DEFUN([OVS_ENABLE_WERROR],
   [AC_ARG_ENABLE(

configure.ac

@@ -185,6 +185,7 @@ OVS_ENABLE_WERROR
 OVS_ENABLE_SPARSE
 OVS_CTAGS_IDENTIFIERS
 OVS_CHECK_DPCLS_AUTOVALIDATOR
+OVS_CHECK_DPIF_AVX512_DEFAULT
 OVS_CHECK_BINUTILS_AVX512
 
 AC_ARG_VAR(KARCH, [Kernel Architecture String])

lib/automake.mk

@@ -116,6 +116,7 @@ lib_libopenvswitch_la_SOURCES = \
 	lib/dpif-netdev-private-dfc.c \
 	lib/dpif-netdev-private-dfc.h \
 	lib/dpif-netdev-private-dpcls.h \
+	lib/dpif-netdev-private-dpif.c \
 	lib/dpif-netdev-private-dpif.h \
 	lib/dpif-netdev-private-flow.h \
 	lib/dpif-netdev-private-thread.h \

lib/dpif-netdev-avx512.c

@@ -24,6 +24,7 @@
 #include "dpif-netdev-perf.h"
 #include "dpif-netdev-private.h"
 
+#include <errno.h>
 #include <immintrin.h>
 
 #include "dp-packet.h"
@@ -57,6 +58,19 @@ struct dpif_userdata {
         struct pkt_flow_meta pkt_meta[NETDEV_MAX_BURST];
 };
 
+int32_t
+dp_netdev_input_outer_avx512_probe(void)
+{
+    bool avx512f_available = dpdk_get_cpu_has_isa("x86_64", "avx512f");
+    bool bmi2_available = dpdk_get_cpu_has_isa("x86_64", "bmi2");
+
+    if (!avx512f_available || !bmi2_available) {
+        return -ENOTSUP;
+    }
+
+    return 0;
+}
+
 int32_t
 dp_netdev_input_outer_avx512(struct dp_netdev_pmd_thread *pmd,
                              struct dp_packet_batch *packets,

lib/dpif-netdev-private-dpif.c

@@ -0,0 +1,124 @@
+/*
+ * Copyright (c) 2021 Intel Corporation.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <config.h>
+
+#include "dpif-netdev-private-dpif.h"
+#include "dpif-netdev-private-thread.h"
+
+#include <errno.h>
+#include <string.h>
+
+#include "openvswitch/dynamic-string.h"
+#include "openvswitch/vlog.h"
+#include "util.h"
+
+VLOG_DEFINE_THIS_MODULE(dpif_netdev_impl);
+
+enum dpif_netdev_impl_info_idx {
+    DPIF_NETDEV_IMPL_SCALAR,
+    DPIF_NETDEV_IMPL_AVX512
+};
+
+/* Actual list of implementations goes here. */
+static struct dpif_netdev_impl_info_t dpif_impls[] = {
+    /* The default scalar C code implementation. */
+    [DPIF_NETDEV_IMPL_SCALAR] = { .input_func = dp_netdev_input,
+      .probe = NULL,
+      .name = "dpif_scalar", },
+
+#if (__x86_64__ && HAVE_AVX512F && HAVE_LD_AVX512_GOOD && __SSE4_2__)
+    /* Only available on x86_64 bit builds with SSE 4.2 used for OVS core. */
+    [DPIF_NETDEV_IMPL_AVX512] = { .input_func = dp_netdev_input_outer_avx512,
+      .probe = dp_netdev_input_outer_avx512_probe,
+      .name = "dpif_avx512", },
+#endif
+};
+
+static dp_netdev_input_func default_dpif_func;
+
+dp_netdev_input_func
+dp_netdev_impl_get_default(void)
+{
+    /* For the first call, this will be NULL. Compute the compile time default.
+     */
+    if (!default_dpif_func) {
+        int dpif_idx = DPIF_NETDEV_IMPL_SCALAR;
+
+/* Configure-time overriding to run test suite on all implementations. */
+#if (__x86_64__ && HAVE_AVX512F && HAVE_LD_AVX512_GOOD && __SSE4_2__)
+#ifdef DPIF_AVX512_DEFAULT
+        dp_netdev_input_func_probe probe;
+
+        /* Check if the compiled default is compatible. */
+        probe = dpif_impls[DPIF_NETDEV_IMPL_AVX512].probe;
+        if (!probe || !probe()) {
+            dpif_idx = DPIF_NETDEV_IMPL_AVX512;
+        }
+#endif
+#endif
+
+        VLOG_INFO("Default DPIF implementation is %s.\n",
+                  dpif_impls[dpif_idx].name);
+        default_dpif_func = dpif_impls[dpif_idx].input_func;
+    }
+
+    return default_dpif_func;
+}
+
+/* This function checks all available DPIF implementations, and selects the
+ * returns the function pointer to the one requested by "name".
+ */
+static int32_t
+dp_netdev_impl_get_by_name(const char *name, dp_netdev_input_func *out_func)
+{
+    ovs_assert(name);
+    ovs_assert(out_func);
+
+    uint32_t i;
+
+    for (i = 0; i < ARRAY_SIZE(dpif_impls); i++) {
+        if (strcmp(dpif_impls[i].name, name) == 0) {
+            /* Probe function is optional - so check it is set before exec. */
+            if (dpif_impls[i].probe) {
+                int probe_err = dpif_impls[i].probe();
+                if (probe_err) {
+                    *out_func = NULL;
+                    return probe_err;
+                }
+            }
+            *out_func = dpif_impls[i].input_func;
+            return 0;
+        }
+    }
+
+    return -EINVAL;
+}
+
+int32_t
+dp_netdev_impl_set_default_by_name(const char *name)
+{
+    dp_netdev_input_func new_default;
+
+    int32_t err = dp_netdev_impl_get_by_name(name, &new_default);
+
+    if (!err) {
+        default_dpif_func = new_default;
+    }
+
+    return err;
+
+}

lib/dpif-netdev-private-dpif.h

@@ -23,7 +23,48 @@
 struct dp_netdev_pmd_thread;
 struct dp_packet_batch;
 
+/* Typedef for DPIF functions.
+ * Returns whether all packets were processed successfully.
+ */
+typedef int32_t (*dp_netdev_input_func)(struct dp_netdev_pmd_thread *pmd,
+                                        struct dp_packet_batch *packets,
+                                        odp_port_t port_no);
+
+/* Probe a DPIF implementation. This allows the implementation to validate CPU
+ * ISA availability. Returns -ENOTSUP if not available, returns 0 if valid to
+ * use.
+ */
+typedef int32_t (*dp_netdev_input_func_probe)(void);
+
+/* Structure describing each available DPIF implementation. */
+struct dpif_netdev_impl_info_t {
+    /* Function pointer to execute to have this DPIF implementation run. */
+    dp_netdev_input_func input_func;
+    /* Function pointer to execute to check the CPU ISA is available to run. If
+     * not necessary, it must be set to NULL which implies that it is always
+     * valid to use. */
+    dp_netdev_input_func_probe probe;
+    /* Name used to select this DPIF implementation. */
+    const char *name;
+};
+
+/* Returns the default DPIF which is first ./configure selected, but can be
+ * overridden at runtime. */
+dp_netdev_input_func dp_netdev_impl_get_default(void);
+
+/* Overrides the default DPIF with the user set DPIF. */
+int32_t dp_netdev_impl_set_default_by_name(const char *name);
+
 /* Available DPIF implementations below. */
+int32_t
+dp_netdev_input(struct dp_netdev_pmd_thread *pmd,
+                struct dp_packet_batch *packets,
+                odp_port_t in_port);
+
+/* AVX512 enabled DPIF implementation and probe functions. */
+int32_t
+dp_netdev_input_outer_avx512_probe(void);
+
 int32_t
 dp_netdev_input_outer_avx512(struct dp_netdev_pmd_thread *pmd,
                              struct dp_packet_batch *packets,

lib/dpif-netdev-private-thread.h

@@ -50,16 +50,6 @@ struct dp_netdev_pmd_thread_ctx {
     bool smc_enable_db;
 };
 
-/* Forward declaration for typedef. */
-struct dp_netdev_pmd_thread;
-
-/* Typedef for DPIF functions.
- * Returns a bitmask of packets to handle, possibly including upcall/misses.
- */
-typedef int32_t (*dp_netdev_input_func)(struct dp_netdev_pmd_thread *pmd,
-                                        struct dp_packet_batch *packets,
-                                        odp_port_t port_no);
-
 /* PMD: Poll modes drivers.  PMD accesses devices via polling to eliminate
  * the performance overhead of interrupt processing.  Therefore netdev can
  * not implement rx-wait for these devices.  dpif-netdev needs to poll

lib/dpif-netdev-unixctl.man

@@ -226,3 +226,6 @@ recirculation (only in balance-tcp mode).
 When this is the case, the above command prints the load-balancing information
 of the bonds configured in datapath \fIdp\fR showing the interface associated
 with each bucket (hash).
+.
+.IP "\fBdpif-netdev/dpif-impl-set\fR \fIdpif_impl\fR"
+Sets the DPIF to be used to \fIdpif_impl\fR. By default "dpif_scalar" is used.

lib/dpif-netdev.c

@@ -469,8 +469,6 @@ static void dp_netdev_execute_actions(struct dp_netdev_pmd_thread *pmd,
                                       const struct flow *flow,
                                       const struct nlattr *actions,
                                       size_t actions_len);
-static int32_t dp_netdev_input(struct dp_netdev_pmd_thread *,
-                            struct dp_packet_batch *, odp_port_t port_no);
 static void dp_netdev_recirculate(struct dp_netdev_pmd_thread *,
                                   struct dp_packet_batch *);
 
@@ -967,6 +965,66 @@ dpif_netdev_subtable_lookup_set(struct unixctl_conn *conn, int argc OVS_UNUSED,
     ds_destroy(&reply);
 }
 
+static void
+dpif_netdev_impl_set(struct unixctl_conn *conn, int argc OVS_UNUSED,
+                     const char *argv[], void *aux OVS_UNUSED)
+{
+    /* This function requires just one parameter, the DPIF name. */
+    const char *dpif_name = argv[1];
+    struct shash_node *node;
+
+    static const char *error_description[2] = {
+        "Unknown DPIF implementation",
+        "CPU doesn't support the required instruction for",
+    };
+
+    ovs_mutex_lock(&dp_netdev_mutex);
+    int32_t err = dp_netdev_impl_set_default_by_name(dpif_name);
+
+    if (err) {
+        struct ds reply = DS_EMPTY_INITIALIZER;
+        ds_put_format(&reply, "DPIF implementation not available: %s %s.\n",
+                      error_description[ (err == -ENOTSUP) ], dpif_name);
+        const char *reply_str = ds_cstr(&reply);
+        unixctl_command_reply_error(conn, reply_str);
+        VLOG_ERR("%s", reply_str);
+        ds_destroy(&reply);
+        ovs_mutex_unlock(&dp_netdev_mutex);
+        return;
+    }
+
+    SHASH_FOR_EACH (node, &dp_netdevs) {
+        struct dp_netdev *dp = node->data;
+
+        /* Get PMD threads list, required to get DPCLS instances. */
+        size_t n;
+        struct dp_netdev_pmd_thread **pmd_list;
+        sorted_poll_thread_list(dp, &pmd_list, &n);
+
+        for (size_t i = 0; i < n; i++) {
+            struct dp_netdev_pmd_thread *pmd = pmd_list[i];
+            if (pmd->core_id == NON_PMD_CORE_ID) {
+                continue;
+            }
+
+            /* Initialize DPIF function pointer to the newly configured
+             * default. */
+            dp_netdev_input_func default_func = dp_netdev_impl_get_default();
+            atomic_uintptr_t *pmd_func = (void *) &pmd->netdev_input_func;
+            atomic_store_relaxed(pmd_func, (uintptr_t) default_func);
+        };
+    }
+    ovs_mutex_unlock(&dp_netdev_mutex);
+
+    /* Reply with success to command. */
+    struct ds reply = DS_EMPTY_INITIALIZER;
+    ds_put_format(&reply, "DPIF implementation set to %s.\n", dpif_name);
+    const char *reply_str = ds_cstr(&reply);
+    unixctl_command_reply(conn, reply_str);
+    VLOG_INFO("%s", reply_str);
+    ds_destroy(&reply);
+}
+
 static void
 dpif_netdev_pmd_rebalance(struct unixctl_conn *conn, int argc,
                           const char *argv[], void *aux OVS_UNUSED)
@@ -1189,6 +1247,10 @@ dpif_netdev_init(void)
     unixctl_command_register("dpif-netdev/subtable-lookup-prio-get", "",
                              0, 0, dpif_netdev_subtable_lookup_get,
                              NULL);
+    unixctl_command_register("dpif-netdev/dpif-impl-set",
+                             "dpif_implementation_name",
+                             1, 1, dpif_netdev_impl_set,
+                             NULL);
     return 0;
 }
 
@@ -6126,8 +6188,10 @@ dp_netdev_configure_pmd(struct dp_netdev_pmd_thread *pmd, struct dp_netdev *dp,
     hmap_init(&pmd->send_port_cache);
     cmap_init(&pmd->tx_bonds);
 
-    /* Initialize the DPIF function pointer to the default scalar version. */
-    pmd->netdev_input_func = dp_netdev_input;
+    /* Initialize DPIF function pointer to the default configured version. */
+    dp_netdev_input_func default_func = dp_netdev_impl_get_default();
+    atomic_uintptr_t *pmd_func = (void *) &pmd->netdev_input_func;
+    atomic_init(pmd_func, (uintptr_t) default_func);
 
     /* init the 'flow_cache' since there is no
      * actual thread created for NON_PMD_CORE_ID. */
@@ -7100,7 +7164,7 @@ dp_netdev_input__(struct dp_netdev_pmd_thread *pmd,
     }
 }
 
-static int32_t
+int32_t
 dp_netdev_input(struct dp_netdev_pmd_thread *pmd,
                 struct dp_packet_batch *packets,
                 odp_port_t port_no)