[PATCH] dumpcap: add lcores option

[Stephen Hemminger <stephen@networkplumber.org>]

The dumpcap application is reading from ring and writing to
the kernel. By default the EAL init will cause the main thread
to bound to the first lcore (cpu 0). Add a command line option
to select the lcore to use; or if no lcores are specified
then just be a normal process and let the CPU scheduler handle it.
Letting scheduler is likely to work well for process doint
I/O with kernel.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 app/dumpcap/main.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/app/dumpcap/main.c b/app/dumpcap/main.c
index ba91ca94d0..879d2b3ea5 100644
--- a/app/dumpcap/main.c
+++ b/app/dumpcap/main.c
@@ -11,6 +11,7 @@
 #include <getopt.h>
 #include <inttypes.h>
 #include <limits.h>
+#include <pthread.h>
 #include <signal.h>
 #include <stdbool.h>
 #include <stdint.h>
@@ -60,6 +61,7 @@ static const char *tmp_dir = "/tmp";
 static unsigned int ring_size = 2048;
 static const char *capture_comment;
 static const char *file_prefix;
+static const char *lcores_arg;
 static bool dump_bpf;
 static bool show_interfaces;
 static bool print_stats;
@@ -343,6 +345,7 @@ static void parse_opts(int argc, char **argv)
 		{ "ifdescr",	     required_argument, NULL, 0 },
 		{ "ifname",	     required_argument, NULL, 0 },
 		{ "interface",       required_argument, NULL, 'i' },
+		{ "lcores",	     required_argument, NULL, 0 },
 		{ "list-interfaces", no_argument,       NULL, 'D' },
 		{ "no-promiscuous-mode", no_argument,   NULL, 'p' },
 		{ "output-file",     required_argument, NULL, 'w' },
@@ -369,6 +372,8 @@ static void parse_opts(int argc, char **argv)
 
 			if (!strcmp(longopt, "capture-comment")) {
 				capture_comment = optarg;
+			} else if (!strcmp(longopt, "lcores")) {
+				lcores_arg = optarg;
 			} else if (!strcmp(longopt, "file-prefix")) {
 				file_prefix = optarg;
 			} else if (!strcmp(longopt, "temp-dir")) {
@@ -608,12 +613,16 @@ static void dpdk_init(void)
 		"--log-level", "notice"
 	};
 	int eal_argc = RTE_DIM(args);
+	cpu_set_t cpuset;
 	char **eal_argv;
 	unsigned int i;
 
 	if (file_prefix != NULL)
 		eal_argc += 2;
 
+	if (lcores_arg != NULL)
+		eal_argc += 2;
+
 	/* DPDK API requires mutable versions of command line arguments. */
 	eal_argv = calloc(eal_argc + 1, sizeof(char *));
 	if (eal_argv == NULL)
@@ -623,6 +632,11 @@ static void dpdk_init(void)
 	for (i = 1; i < RTE_DIM(args); i++)
 		eal_argv[i] = strdup(args[i]);
 
+	if (lcores_arg != NULL) {
+		eal_argv[i++] = strdup("--lcores");
+		eal_argv[i++] = strdup(lcores_arg);
+	}
+
 	if (file_prefix != NULL) {
 		eal_argv[i++] = strdup("--file-prefix");
 		eal_argv[i++] = strdup(file_prefix);
@@ -633,8 +647,24 @@ static void dpdk_init(void)
 			rte_panic("No memory\n");
 	}
 
+	if (pthread_getaffinity_np(pthread_self(), sizeof(cpuset), &cpuset) < 0)
+		rte_panic("pthread_getaffinity failed\n");
+
 	if (rte_eal_init(eal_argc, eal_argv) < 0)
 		rte_exit(EXIT_FAILURE, "EAL init failed: is primary process running?\n");
+
+	/*
+	 * If no lcores argument was speciried, then run this program as a normal process
+	 * which can be scheduled on any non-isolated CPU.
+	 *
+	 * EAL init will cause this thread to be assigned to the first lcore
+	 * which is not what what we want for this secondary process that will
+	 * be interacting with the Linux kernel.
+	 */
+	if (lcores_arg == NULL) {
+		if (pthread_setaffinity_np(pthread_self(), sizeof(cpuset), &cpuset) < 0)
+			perror("pthread_setaffinity");
+	}
 }
 
 /* Create packet ring shared between callbacks and process */
-- 
2.43.0