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diff --git a/docs/requirements/03-dpdk_ka.rst b/docs/requirements/03-dpdk_ka.rst new file mode 100644 index 00000000..b20b4cd3 --- /dev/null +++ b/docs/requirements/03-dpdk_ka.rst @@ -0,0 +1,124 @@ +DPDK Keep Alive Overview +========================= +SFQM aims to enable fault detection within DPDK, the very first feature to +meet this goal is the DPDK Keep Alive Sample app that is part of DPDK 2.2. + +DPDK Keep Alive or KA is a sample application that acts as a heartbeat/watchdog +for DPDK packet processing cores, to detect application thread failure. The +application supports the detection of ‘failed’ DPDK cores and notification to a +HA/SA middleware. The purpose is to detect Packet Processing Core fails (e.g. +infinite loop) and ensure the failure of the core does not result in a fault +that is not detectable by a management entity. + +.. Figure:: dpdk_ka.png + + DPDK Keep Alive Sample Application + +Essentially the app demonstrates how to detect 'silent outages' on DPDK packet +processing cores. The application can be decomposed into two specific parts: +detection and notification. + +* The detection period is programmable/configurable but defaults to 5ms if no + timeout is specified. +* The Notification support is enabled by simply having a hook function that where this + can be 'call back support' for a fault management application with a compliant + heartbeat mechanism. + +DPDK Keep Alive Sample App Internals +==================================== +This section provides some explanation of the The Keep-Alive/'Liveliness' +conceptual scheme as well as the DPDK Keep Alive App. The initialization and +run-time paths are very similar to those of the L2 forwarding application (see +`L2 Forwarding Sample Application (in Real and Virtualized Environments)`_ for more +information). + +There are two types of cores: a Keep Alive Monitor Agent Core (master DPDK core) +and Worker cores (Tx/Rx/Forwarding cores). The Keep Alive Monitor Agent Core +will supervise worker cores and report any failure (2 successive missed pings). +The Keep-Alive/'Liveliness' conceptual scheme is: + +* DPDK worker cores mark their liveliness as they forward traffic. +* A Keep Alive Monitor Agent Core runs a function every N Milliseconds to + inspect worker core liveliness. +* If keep-alive agent detects time-outs, it notifies the fault management + entity through a call-back function. + +**Note:** Only the worker cores state is monitored. There is no mechanism or agent +to monitor the Keep Alive Monitor Agent Core. + +DPDK Keep Alive Sample App Code Internals +========================================= +The following section provides some explanation of the code aspects that are +specific to the Keep Alive sample application. + +The heartbeat functionality is initialized with a struct rte_heartbeat and the +callback function to invoke in the case of a timeout. + +.. code:: c + + rte_global_keepalive_info = rte_keepalive_create(&dead_core, NULL); + if (rte_global_hbeat_info == NULL) + rte_exit(EXIT_FAILURE, "keepalive_create() failed"); + +The function that issues the pings hbeat_dispatch_pings() is configured to run +every check_period milliseconds. + +.. code:: c + + if (rte_timer_reset(&hb_timer, + (check_period * rte_get_timer_hz()) / 1000, + PERIODICAL, + rte_lcore_id(), + &hbeat_dispatch_pings, rte_global_keepalive_info + ) != 0 ) + rte_exit(EXIT_FAILURE, "Keepalive setup failure.\n"); + +The rest of the initialization and run-time path follows the same paths as the +the L2 forwarding application. The only addition to the main processing loop is +the mark alive functionality and the example random failures. + +.. code:: c + + rte_keepalive_mark_alive(&rte_global_hbeat_info); + cur_tsc = rte_rdtsc(); + + /* Die randomly within 7 secs for demo purposes.. */ + if (cur_tsc - tsc_initial > tsc_lifetime) + break; + +The rte_keepalive_mark_alive() function simply sets the core state to alive. + +.. code:: c + + static inline void + rte_keepalive_mark_alive(struct rte_heartbeat *keepcfg) + { + keepcfg->state_flags[rte_lcore_id()] = 1; + } + +Keep Alive Monitor Agent Core Monitoring Options +The application can run on either a host or a guest. As such there are a number +of options for monitoring the Keep Alive Monitor Agent Core through a Local +Agent on the compute node: + + ====================== ========== ============= + Application Location DPDK KA LOCAL AGENT + ====================== ========== ============= + HOST X HOST/GUEST + GUEST X HOST/GUEST + ====================== ========== ============= + + +For the first implementation of a Local Agent SFQM will enable: + + ====================== ========== ============= + Application Location DPDK KA LOCAL AGENT + ====================== ========== ============= + HOST X HOST + ====================== ========== ============= + +Through extending the dpdkstat plugin for collectd with KA functionality, and +integrating the extended plugin with Monasca for high performing, resilient, +and scalable fault detection. + +.. _L2 Forwarding Sample Application (in Real and Virtualized Environments): http://dpdk.org/doc/guides/sample_app_ug/l2_forward_real_virtual.html |