[PATCH v2] 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>
---
v2 - fix typos
   - name it "--lcore" since dumpcap only uses single lcore
   - use rte_thread instead of pthread
   
 app/dumpcap/main.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/app/dumpcap/main.c b/app/dumpcap/main.c
index ba91ca94d0..cb2a439f79 100644
--- a/app/dumpcap/main.c
+++ b/app/dumpcap/main.c
@@ -38,6 +38,7 @@
 #include <rte_pdump.h>
 #include <rte_ring.h>
 #include <rte_string_fns.h>
+#include <rte_thread.h>
 #include <rte_time.h>
 #include <rte_version.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 *lcore_arg;
 static bool dump_bpf;
 static bool show_interfaces;
 static bool print_stats;
@@ -143,6 +145,7 @@ static void usage(void)
 	       "                           (default: /tmp)\n"
 	       "\n"
 	       "Miscellaneous:\n"
+	       "  --lcore=<core>	   cpu core to run on (default: any)\n"
 	       "  --file-prefix=<prefix>   prefix to use for multi-process\n"
 	       "  -q                       don't report packet capture counts\n"
 	       "  -v, --version            print version information and exit\n"
@@ -343,6 +346,7 @@ static void parse_opts(int argc, char **argv)
 		{ "ifdescr",	     required_argument, NULL, 0 },
 		{ "ifname",	     required_argument, NULL, 0 },
 		{ "interface",       required_argument, NULL, 'i' },
+		{ "lcore",	     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 +373,8 @@ static void parse_opts(int argc, char **argv)
 
 			if (!strcmp(longopt, "capture-comment")) {
 				capture_comment = optarg;
+			} else if (!strcmp(longopt, "lcore")) {
+				lcore_arg = optarg;
 			} else if (!strcmp(longopt, "file-prefix")) {
 				file_prefix = optarg;
 			} else if (!strcmp(longopt, "temp-dir")) {
@@ -608,12 +614,16 @@ static void dpdk_init(void)
 		"--log-level", "notice"
 	};
 	int eal_argc = RTE_DIM(args);
+	rte_cpuset_t cpuset = { };
 	char **eal_argv;
 	unsigned int i;
 
 	if (file_prefix != NULL)
 		eal_argc += 2;
 
+	if (lcore_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 +633,11 @@ static void dpdk_init(void)
 	for (i = 1; i < RTE_DIM(args); i++)
 		eal_argv[i] = strdup(args[i]);
 
+	if (lcore_arg != NULL) {
+		eal_argv[i++] = strdup("--lcores");
+		eal_argv[i++] = strdup(lcore_arg);
+	}
+
 	if (file_prefix != NULL) {
 		eal_argv[i++] = strdup("--file-prefix");
 		eal_argv[i++] = strdup(file_prefix);
@@ -633,8 +648,24 @@ static void dpdk_init(void)
 			rte_panic("No memory\n");
 	}
 
+	/*
+	 * Need to get the original cpuset, before EAL init changes
+	 * the affinity of this thread (main lcore).
+	 */
+	if (lcore_arg == NULL &&
+	    rte_thread_get_affinity_by_id(rte_thread_self(), &cpuset) != 0)
+		rte_panic("rte_thread_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 lcore argument was specified, then run this program as a normal process
+	 * which can be scheduled on any non-isolated CPU.
+	 */
+	if (lcore_arg == NULL &&
+	    rte_thread_set_affinity_by_id(rte_thread_self(), &cpuset) != 0)
+		rte_exit(EXIT_FAILURE, "Can not restore original cpu affinity\n");
 }
 
 /* Create packet ring shared between callbacks and process */
-- 
2.43.0