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GET /api/patches/1525733/?format=api
{ "id": 1525733, "url": "http://patchwork.ozlabs.org/api/patches/1525733/?format=api", "web_url": "http://patchwork.ozlabs.org/project/openvswitch/patch/0d917810d36ddb53c378b5615fa7fb8e9f193215.1631094144.git.grive@u256.net/", "project": { "id": 47, "url": "http://patchwork.ozlabs.org/api/projects/47/?format=api", "name": "Open vSwitch", "link_name": "openvswitch", "list_id": "ovs-dev.openvswitch.org", "list_email": "ovs-dev@openvswitch.org", "web_url": "http://openvswitch.org/", "scm_url": "git@github.com:openvswitch/ovs.git", "webscm_url": "https://github.com/openvswitch/ovs", "list_archive_url": "", "list_archive_url_format": "", "commit_url_format": "" }, "msgid": "<0d917810d36ddb53c378b5615fa7fb8e9f193215.1631094144.git.grive@u256.net>", "list_archive_url": null, "date": "2021-09-08T09:47:47", "name": "[ovs-dev,v5,23/27] dpif-netdev: Use lockless queue to manage offloads", "commit_ref": "ec4ac625888e9f7a10e1b8be6b94f85dc48f6336", "pull_url": null, "state": "accepted", "archived": false, "hash": "b01b707f1cb77e3ede0eeae7fa933bfee68b8af5", "submitter": { "id": 78795, "url": "http://patchwork.ozlabs.org/api/people/78795/?format=api", "name": "Gaetan Rivet", "email": "grive@u256.net" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/openvswitch/patch/0d917810d36ddb53c378b5615fa7fb8e9f193215.1631094144.git.grive@u256.net/mbox/", "series": [ { "id": 261424, "url": "http://patchwork.ozlabs.org/api/series/261424/?format=api", "web_url": "http://patchwork.ozlabs.org/project/openvswitch/list/?series=261424", "date": "2021-09-08T09:47:24", "name": "dpif-netdev: Parallel offload processing", "version": 5, "mbox": "http://patchwork.ozlabs.org/series/261424/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/1525733/comments/", "check": "success", "checks": "http://patchwork.ozlabs.org/api/patches/1525733/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "<ovs-dev-bounces@openvswitch.org>", "X-Original-To": [ "incoming@patchwork.ozlabs.org", "ovs-dev@openvswitch.org" ], "Delivered-To": [ "patchwork-incoming@bilbo.ozlabs.org", "ovs-dev@lists.linuxfoundation.org" ], "Authentication-Results": [ "ozlabs.org;\n\tdkim=fail reason=\"signature verification failed\" (2048-bit key;\n unprotected) header.d=u256.net header.i=@u256.net header.a=rsa-sha256\n header.s=fm2 header.b=btEbuYGb;\n\tdkim=fail reason=\"signature verification failed\" (2048-bit key;\n unprotected) header.d=messagingengine.com header.i=@messagingengine.com\n header.a=rsa-sha256 header.s=fm3 header.b=bTTz4bS7;\n\tdkim-atps=neutral", "ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=openvswitch.org\n (client-ip=140.211.166.133; 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charset=\"us-ascii\"", "Content-Transfer-Encoding": "7bit", "Errors-To": "ovs-dev-bounces@openvswitch.org", "Sender": "\"dev\" <ovs-dev-bounces@openvswitch.org>" }, "content": "The dataplane threads (PMDs) send offloading commands to a dedicated\noffload management thread. The current implementation uses a lock\nand benchmarks show a high contention on the queue in some cases.\n\nWith high-contention, the mutex will more often lead to the locking\nthread yielding in wait, using a syscall. This should be avoided in\na userland dataplane.\n\nThe mpsc-queue can be used instead. It uses less cycles and has\nlower latency. Benchmarks show better behavior as multiple\nrevalidators and one or multiple PMDs writes to a single queue\nwhile another thread polls it.\n\nOne trade-off with the new scheme however is to be forced to poll\nthe queue from the offload thread. Without mutex, a cond_wait\ncannot be used for signaling. The offload thread is implementing\nan exponential backoff and will sleep in short increments when no\ndata is available. This makes the thread yield, at the price of\nsome latency to manage offloads after an inactivity period.\n\nSigned-off-by: Gaetan Rivet <grive@u256.net>\nReviewed-by: Eli Britstein <elibr@nvidia.com>\nReviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>\n---\n lib/dpif-netdev.c | 109 ++++++++++++++++++++++++----------------------\n 1 file changed, 57 insertions(+), 52 deletions(-)", "diff": "diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c\nindex bf5785981..4e91926fd 100644\n--- a/lib/dpif-netdev.c\n+++ b/lib/dpif-netdev.c\n@@ -55,6 +55,7 @@\n #include \"id-pool.h\"\n #include \"ipf.h\"\n #include \"mov-avg.h\"\n+#include \"mpsc-queue.h\"\n #include \"netdev.h\"\n #include \"netdev-offload.h\"\n #include \"netdev-provider.h\"\n@@ -366,25 +367,22 @@ union dp_offload_thread_data {\n };\n \n struct dp_offload_thread_item {\n- struct ovs_list node;\n+ struct mpsc_queue_node node;\n enum dp_offload_type type;\n long long int timestamp;\n union dp_offload_thread_data data[0];\n };\n \n struct dp_offload_thread {\n- struct ovs_mutex mutex;\n- struct ovs_list list;\n- uint64_t enqueued_item;\n+ struct mpsc_queue queue;\n+ atomic_uint64_t enqueued_item;\n struct mov_avg_cma cma;\n struct mov_avg_ema ema;\n- pthread_cond_t cond;\n };\n \n static struct dp_offload_thread dp_offload_thread = {\n- .mutex = OVS_MUTEX_INITIALIZER,\n- .list = OVS_LIST_INITIALIZER(&dp_offload_thread.list),\n- .enqueued_item = 0,\n+ .queue = MPSC_QUEUE_INITIALIZER(&dp_offload_thread.queue),\n+ .enqueued_item = ATOMIC_VAR_INIT(0),\n .cma = MOV_AVG_CMA_INITIALIZER,\n .ema = MOV_AVG_EMA_INITIALIZER(100),\n };\n@@ -2616,11 +2614,8 @@ dp_netdev_free_offload(struct dp_offload_thread_item *offload)\n static void\n dp_netdev_append_offload(struct dp_offload_thread_item *offload)\n {\n- ovs_mutex_lock(&dp_offload_thread.mutex);\n- ovs_list_push_back(&dp_offload_thread.list, &offload->node);\n- dp_offload_thread.enqueued_item++;\n- xpthread_cond_signal(&dp_offload_thread.cond);\n- ovs_mutex_unlock(&dp_offload_thread.mutex);\n+ mpsc_queue_insert(&dp_offload_thread.queue, &offload->node);\n+ atomic_count_inc64(&dp_offload_thread.enqueued_item);\n }\n \n static int\n@@ -2765,58 +2760,68 @@ dp_offload_flush(struct dp_offload_thread_item *item)\n ovs_barrier_block(flush->barrier);\n }\n \n+#define DP_NETDEV_OFFLOAD_BACKOFF_MIN 1\n+#define DP_NETDEV_OFFLOAD_BACKOFF_MAX 64\n #define DP_NETDEV_OFFLOAD_QUIESCE_INTERVAL_US (10 * 1000) /* 10 ms */\n \n static void *\n dp_netdev_flow_offload_main(void *data OVS_UNUSED)\n {\n struct dp_offload_thread_item *offload;\n- struct ovs_list *list;\n+ struct mpsc_queue_node *node;\n+ struct mpsc_queue *queue;\n long long int latency_us;\n long long int next_rcu;\n long long int now;\n+ uint64_t backoff;\n \n- next_rcu = time_usec() + DP_NETDEV_OFFLOAD_QUIESCE_INTERVAL_US;\n- for (;;) {\n- ovs_mutex_lock(&dp_offload_thread.mutex);\n- if (ovs_list_is_empty(&dp_offload_thread.list)) {\n- ovsrcu_quiesce_start();\n- ovs_mutex_cond_wait(&dp_offload_thread.cond,\n- &dp_offload_thread.mutex);\n- ovsrcu_quiesce_end();\n- next_rcu = time_usec() + DP_NETDEV_OFFLOAD_QUIESCE_INTERVAL_US;\n- }\n- list = ovs_list_pop_front(&dp_offload_thread.list);\n- dp_offload_thread.enqueued_item--;\n- offload = CONTAINER_OF(list, struct dp_offload_thread_item, node);\n- ovs_mutex_unlock(&dp_offload_thread.mutex);\n-\n- switch (offload->type) {\n- case DP_OFFLOAD_FLOW:\n- dp_offload_flow(offload);\n- break;\n- case DP_OFFLOAD_FLUSH:\n- dp_offload_flush(offload);\n- break;\n- default:\n- OVS_NOT_REACHED();\n+ queue = &dp_offload_thread.queue;\n+ mpsc_queue_acquire(queue);\n+\n+ while (true) {\n+ backoff = DP_NETDEV_OFFLOAD_BACKOFF_MIN;\n+ while (mpsc_queue_tail(queue) == NULL) {\n+ xnanosleep(backoff * 1E6);\n+ if (backoff < DP_NETDEV_OFFLOAD_BACKOFF_MAX) {\n+ backoff <<= 1;\n+ }\n }\n \n- now = time_usec();\n+ next_rcu = time_usec() + DP_NETDEV_OFFLOAD_QUIESCE_INTERVAL_US;\n+ MPSC_QUEUE_FOR_EACH_POP (node, queue) {\n+ offload = CONTAINER_OF(node, struct dp_offload_thread_item, node);\n+ atomic_count_dec64(&dp_offload_thread.enqueued_item);\n \n- latency_us = now - offload->timestamp;\n- mov_avg_cma_update(&dp_offload_thread.cma, latency_us);\n- mov_avg_ema_update(&dp_offload_thread.ema, latency_us);\n+ switch (offload->type) {\n+ case DP_OFFLOAD_FLOW:\n+ dp_offload_flow(offload);\n+ break;\n+ case DP_OFFLOAD_FLUSH:\n+ dp_offload_flush(offload);\n+ break;\n+ default:\n+ OVS_NOT_REACHED();\n+ }\n \n- dp_netdev_free_offload(offload);\n+ now = time_usec();\n \n- /* Do RCU synchronization at fixed interval. */\n- if (now > next_rcu) {\n- ovsrcu_quiesce();\n- next_rcu = time_usec() + DP_NETDEV_OFFLOAD_QUIESCE_INTERVAL_US;\n+ latency_us = now - offload->timestamp;\n+ mov_avg_cma_update(&dp_offload_thread.cma, latency_us);\n+ mov_avg_ema_update(&dp_offload_thread.ema, latency_us);\n+\n+ dp_netdev_free_offload(offload);\n+\n+ /* Do RCU synchronization at fixed interval. */\n+ if (now > next_rcu) {\n+ ovsrcu_quiesce();\n+ next_rcu = time_usec() + DP_NETDEV_OFFLOAD_QUIESCE_INTERVAL_US;\n+ }\n }\n }\n \n+ OVS_NOT_REACHED();\n+ mpsc_queue_release(queue);\n+\n return NULL;\n }\n \n@@ -2827,7 +2832,7 @@ queue_netdev_flow_del(struct dp_netdev_pmd_thread *pmd,\n struct dp_offload_thread_item *offload;\n \n if (ovsthread_once_start(&offload_thread_once)) {\n- xpthread_cond_init(&dp_offload_thread.cond, NULL);\n+ mpsc_queue_init(&dp_offload_thread.queue);\n ovs_thread_create(\"hw_offload\", dp_netdev_flow_offload_main, NULL);\n ovsthread_once_done(&offload_thread_once);\n }\n@@ -2917,7 +2922,7 @@ queue_netdev_flow_put(struct dp_netdev_pmd_thread *pmd,\n }\n \n if (ovsthread_once_start(&offload_thread_once)) {\n- xpthread_cond_init(&dp_offload_thread.cond, NULL);\n+ mpsc_queue_init(&dp_offload_thread.queue);\n ovs_thread_create(\"hw_offload\", dp_netdev_flow_offload_main, NULL);\n ovsthread_once_done(&offload_thread_once);\n }\n@@ -2969,7 +2974,7 @@ dp_netdev_offload_flush_enqueue(struct dp_netdev *dp,\n struct dp_offload_flush_item *flush;\n \n if (ovsthread_once_start(&offload_thread_once)) {\n- xpthread_cond_init(&dp_offload_thread.cond, NULL);\n+ mpsc_queue_init(&dp_offload_thread.queue);\n ovs_thread_create(\"hw_offload\", dp_netdev_flow_offload_main, NULL);\n ovsthread_once_done(&offload_thread_once);\n }\n@@ -4389,8 +4394,8 @@ dpif_netdev_offload_stats_get(struct dpif *dpif,\n }\n ovs_mutex_unlock(&dp->port_mutex);\n \n- stats->counters[DP_NETDEV_HW_OFFLOADS_STATS_ENQUEUED].value =\n- dp_offload_thread.enqueued_item;\n+ atomic_read_relaxed(&dp_offload_thread.enqueued_item,\n+ &stats->counters[DP_NETDEV_HW_OFFLOADS_STATS_ENQUEUED].value);\n stats->counters[DP_NETDEV_HW_OFFLOADS_STATS_INSERTED].value = nb_offloads;\n stats->counters[DP_NETDEV_HW_OFFLOADS_STATS_LAT_CMA_MEAN].value =\n mov_avg_cma(&dp_offload_thread.cma);\n", "prefixes": [ "ovs-dev", "v5", "23/27" ] }