12. Keep Alive Sample Application

The Keep Alive application is a simple example of a heartbeat/watchdog for packet processing cores. It demonstrates how to detect ‘failed’ DPDK cores and notify a fault management entity of this failure. Its purpose is to ensure the failure of the core does not result in a fault that is not detectable by a management entity.

12.1. Overview

The application demonstrates how to protect against ‘silent outages’ on packet processing cores. A Keep Alive Monitor Agent Core (main) monitors the state of packet processing cores (worker cores) by dispatching pings at a regular time interval (default is 5ms) and monitoring the state of the cores. Cores states are: Alive, MIA, Dead or Buried. MIA indicates a missed ping, and Dead indicates two missed pings within the specified time interval. When a core is Dead, a callback function is invoked to restart the packet processing core; A real life application might use this callback function to notify a higher level fault management entity of the core failure in order to take the appropriate corrective action.

Note: Only the worker cores are monitored. A local (on the host) mechanism or agent to supervise the Keep Alive Monitor Agent Core DPDK core is required to detect its failure.

Note: This application is based on the L2 Forwarding Sample Application (in Real and Virtualized Environments). As such, the initialization and run-time paths are very similar to those of the L2 forwarding application.

12.2. Compiling the Application

To compile the sample application, see Compiling the Sample Applications.

The application is located in the l2fwd_keep_alive sub-directory.

12.3. Running the Application

The application has a number of command line options:

./<build_dir>/examples/dpdk-l2fwd-keepalive [EAL options] \
        -- -p PORTMASK [-q NQ] [-K PERIOD] [-T PERIOD]

where,

  • p PORTMASK: A hexadecimal bitmask of the ports to configure

  • q NQ: Maximum number of queues per lcore (default is 1)

  • K PERIOD: Heartbeat check period in ms(5ms default; 86400 max)

  • T PERIOD: statistics will be refreshed each PERIOD seconds (0 to disable, 10 default, 86400 maximum).

To run the application in linux environment with 4 lcores, 16 ports 8 RX queues per lcore and a ping interval of 10ms, issue the command:

./<build_dir>/examples/dpdk-l2fwd-keepalive -l 0-3 -n 4 -- -q 8 -p ffff -K 10

Refer to the DPDK Getting Started Guide for general information on running applications and the Environment Abstraction Layer (EAL) options.

12.4. Explanation

The following sections provide explanation of the Keep-Alive/’Liveliness’ conceptual scheme. As mentioned in the overview section, the initialization and run-time paths are very similar to those of the L2 Forwarding Sample Application (in Real and Virtualized Environments).

The Keep-Alive/’Liveliness’ conceptual scheme:

  • A Keep- Alive Agent Runs every N Milliseconds.

  • DPDK Cores respond to the keep-alive agent.

  • If a keep-alive agent detects time-outs, it notifies the fault management entity through a callback function.

The following sections provide explanation of the code aspects that are specific to the Keep Alive sample application.

The keepalive functionality is initialized with a struct rte_keepalive and the callback function to invoke in the case of a timeout.

rte_global_keepalive_info =
	rte_keepalive_create(&dead_core, ka_shm);
if (rte_global_keepalive_info == NULL)
	rte_exit(EXIT_FAILURE, "init_keep_alive() failed");

The function that issues the pings keepalive_dispatch_pings() is configured to run every check_period milliseconds.

if (rte_timer_reset(&stats_timer,
		(timer_period * rte_get_timer_hz()) / 1000,
		PERIODICAL,
		rte_lcore_id(),
		&print_stats, NULL
		) != 0 )
	rte_exit(EXIT_FAILURE, "Stats setup failure.\n");

The rest of the initialization and run-time paths follow the same paths as the L2 forwarding application. The only addition to the main processing loop is the mark alive functionality and the example random failures.

rte_keepalive_mark_alive(rte_global_keepalive_info);

cur_tsc = rte_rdtsc();

/*
 * Die randomly within 7 secs for demo purposes if
 * keepalive enabled
 */
if (check_period > 0 && cur_tsc - tsc_initial > tsc_lifetime)
	break;

The rte_keepalive_mark_alive function simply sets the core state to alive.

static inline void
rte_keepalive_mark_alive(struct rte_keepalive *keepcfg)
{
    keepcfg->live_data[rte_lcore_id()].core_state = RTE_KA_STATE_ALIVE;
}