dpif-netdev: Add study function to select the best mfex function

The study function runs all the available implementations
of miniflow_extract and makes a choice whose hitmask has
maximum hits and sets the mfex to that function.

Study can be run at runtime using the following command:

$ ovs-appctl dpif-netdev/miniflow-parser-set study

Signed-off-by: Kumar Amber <kumar.amber@intel.com>
Co-authored-by: Harry van Haaren <harry.van.haaren@intel.com>
Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
Acked-by: Eelco Chaudron <echaudro@redhat.com>
Acked-by: Flavio Leitner <fbl@sysclose.org>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>

NEWS

@@ -38,6 +38,9 @@ Post-v2.15.0
      * Add command line option to switch between MFEX function pointers.
      * Add miniflow extract auto-validator function to compare different
        miniflow extract implementations against default implementation.
+     * Add study function to miniflow function table which studies packet
+       and automatically chooses the best miniflow implementation for that
+       traffic.
    - ovs-ctl:
      * New option '--no-record-hostname' to disable hostname configuration
        in ovsdb on startup.

lib/automake.mk

@@ -107,6 +107,7 @@ lib_libopenvswitch_la_SOURCES = \
 	lib/dp-packet.h \
 	lib/dp-packet.c \
 	lib/dpdk.h \
+	lib/dpif-netdev-extract-study.c \
 	lib/dpif-netdev-lookup.h \
 	lib/dpif-netdev-lookup.c \
 	lib/dpif-netdev-lookup-autovalidator.c \

lib/dpif-netdev-extract-study.c

@@ -0,0 +1,135 @@
+/*
+ * Copyright (c) 2021 Intel.
+ *
+ * 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 <errno.h>
+#include <stdint.h>
+#include <string.h>
+
+#include "dpif-netdev-private-thread.h"
+#include "openvswitch/vlog.h"
+#include "ovs-thread.h"
+
+VLOG_DEFINE_THIS_MODULE(dpif_mfex_extract_study);
+
+static atomic_uint32_t mfex_study_pkts_count = 0;
+
+/* Struct to hold miniflow study stats. */
+struct study_stats {
+    uint32_t pkt_count;
+    uint32_t impl_hitcount[MFEX_IMPL_MAX];
+};
+
+/* Define per thread data to hold the study stats. */
+DEFINE_PER_THREAD_MALLOCED_DATA(struct study_stats *, study_stats);
+
+/* Allocate per thread PMD pointer space for study_stats. */
+static inline struct study_stats *
+mfex_study_get_study_stats_ptr(void)
+{
+    struct study_stats *stats = study_stats_get();
+    if (OVS_UNLIKELY(!stats)) {
+        stats = xzalloc(sizeof *stats);
+        study_stats_set_unsafe(stats);
+    }
+    return stats;
+}
+
+uint32_t
+mfex_study_traffic(struct dp_packet_batch *packets,
+                   struct netdev_flow_key *keys,
+                   uint32_t keys_size, odp_port_t in_port,
+                   struct dp_netdev_pmd_thread *pmd_handle)
+{
+    uint32_t hitmask = 0;
+    uint32_t mask = 0;
+    struct dp_netdev_pmd_thread *pmd = pmd_handle;
+    struct dpif_miniflow_extract_impl *miniflow_funcs;
+    struct study_stats *stats = mfex_study_get_study_stats_ptr();
+    miniflow_funcs = dpif_mfex_impl_info_get();
+
+    /* Run traffic optimized miniflow_extract to collect the hitmask
+     * to be compared after certain packets have been hit to choose
+     * the best miniflow_extract version for that traffic.
+     */
+    for (int i = MFEX_IMPL_START_IDX; i < MFEX_IMPL_MAX; i++) {
+        if (!miniflow_funcs[i].available) {
+            continue;
+        }
+
+        hitmask = miniflow_funcs[i].extract_func(packets, keys, keys_size,
+                                                 in_port, pmd_handle);
+        stats->impl_hitcount[i] += count_1bits(hitmask);
+
+        /* If traffic is not classified then we dont overwrite the keys
+         * array in minfiflow implementations so its safe to create a
+         * mask for all those packets whose miniflow have been created.
+         */
+        mask |= hitmask;
+    }
+
+    stats->pkt_count += dp_packet_batch_size(packets);
+
+    /* Choose the best implementation after a minimum packets have been
+     * processed.
+     */
+    if (stats->pkt_count >= MFEX_MAX_PKT_COUNT) {
+        uint32_t best_func_index = MFEX_IMPL_START_IDX;
+        uint32_t max_hits = 0;
+        for (int i = MFEX_IMPL_START_IDX; i < MFEX_IMPL_MAX; i++) {
+            if (stats->impl_hitcount[i] > max_hits) {
+                max_hits = stats->impl_hitcount[i];
+                best_func_index = i;
+            }
+        }
+
+        /* If 50% of the packets hit, enable the function. */
+        if (max_hits >= (mfex_study_pkts_count / 2)) {
+            miniflow_extract_func mf_func =
+                        miniflow_funcs[best_func_index].extract_func;
+            atomic_uintptr_t *pmd_func = (void *)&pmd->miniflow_extract_opt;
+            atomic_store_relaxed(pmd_func, (uintptr_t) mf_func);
+            VLOG_INFO("MFEX study chose impl %s: (hits %u/%u pkts)",
+                      miniflow_funcs[best_func_index].name, max_hits,
+                      stats->pkt_count);
+        } else {
+            /* Set the implementation to null for default miniflow. */
+            miniflow_extract_func mf_func =
+                        miniflow_funcs[MFEX_IMPL_SCALAR].extract_func;
+            atomic_uintptr_t *pmd_func = (void *)&pmd->miniflow_extract_opt;
+            atomic_store_relaxed(pmd_func, (uintptr_t) mf_func);
+            VLOG_INFO("Not enough packets matched (%u/%u), disabling"
+                      " optimized MFEX.", max_hits, stats->pkt_count);
+        }
+
+        /* In debug mode show stats for all the counters. */
+        if (VLOG_IS_DBG_ENABLED()) {
+
+            for (int i = MFEX_IMPL_START_IDX; i < MFEX_IMPL_MAX; i++) {
+                VLOG_DBG("MFEX study results for implementation %s:"
+                         " (hits %u/%u pkts)", miniflow_funcs[i].name,
+                         stats->impl_hitcount[i], stats->pkt_count);
+            }
+        }
+
+        /* Reset stats so that study function can be called again
+         * for next traffic type and optimal function ptr can be
+         * chosen.
+         */
+        memset(stats, 0, sizeof(struct study_stats));
+    }
+    return mask;
+}

lib/dpif-netdev-private-extract.c

@@ -47,6 +47,11 @@ static struct dpif_miniflow_extract_impl mfex_impls[] = {
         .probe = NULL,
         .extract_func = NULL,
         .name = "scalar", },
+
+    [MFEX_IMPL_STUDY] = {
+        .probe = NULL,
+        .extract_func = mfex_study_traffic,
+        .name = "study", },
 };
 
 BUILD_ASSERT_DECL(MFEX_IMPL_MAX == ARRAY_SIZE(mfex_impls));
@@ -166,6 +171,13 @@ dp_mfex_impl_get_by_name(const char *name, miniflow_extract_func *out_func)
     return -ENOENT;
 }
 
+struct dpif_miniflow_extract_impl *
+dpif_mfex_impl_info_get(void) {
+
+    return mfex_impls;
+
+}
+
 uint32_t
 dpif_miniflow_extract_autovalidator(struct dp_packet_batch *packets,
                                     struct netdev_flow_key *keys,

lib/dpif-netdev-private-extract.h

@@ -80,6 +80,7 @@ struct dpif_miniflow_extract_impl {
 enum dpif_miniflow_extract_impl_idx {
     MFEX_IMPL_AUTOVALIDATOR,
     MFEX_IMPL_SCALAR,
+    MFEX_IMPL_STUDY,
     MFEX_IMPL_MAX
 };
 
@@ -91,6 +92,9 @@ extern struct ovs_mutex dp_netdev_mutex;
 
 #define MFEX_IMPL_START_IDX MFEX_IMPL_MAX
 
+/* Max count of packets to be compared. */
+#define MFEX_MAX_PKT_COUNT (128)
+
 /* This function returns all available implementations to the caller. The
  * quantity of implementations is returned by the int return value.
  */
@@ -111,6 +115,9 @@ miniflow_extract_func dp_mfex_impl_get_default(void);
 /* Overrides the default MFEX with the user set MFEX. */
 int dp_mfex_impl_set_default_by_name(const char *name);
 
+/* Retrieve the array of miniflow implementations for iteration. */
+struct dpif_miniflow_extract_impl *
+dpif_mfex_impl_info_get(void);
 
 /* Initializes the available miniflow extract implementations by probing for
  * the CPU ISA requirements. As the runtime available CPU ISA does not change
@@ -132,4 +139,16 @@ dpif_miniflow_extract_autovalidator(struct dp_packet_batch *batch,
                                     uint32_t keys_size, odp_port_t in_port,
                                     struct dp_netdev_pmd_thread *pmd_handle);
 
+/* Retrieve the number of packets by studying packets using different miniflow
+ * implementations to choose the best implementation using the maximum hitmask
+ * count.
+ * On error, returns a zero for no packets.
+ * On success, returns mask of the packets hit.
+ */
+uint32_t
+mfex_study_traffic(struct dp_packet_batch *packets,
+                   struct netdev_flow_key *keys,
+                   uint32_t keys_size, odp_port_t in_port,
+                   struct dp_netdev_pmd_thread *pmd_handle);
+
 #endif /* MFEX_AVX512_EXTRACT */