netstacklat: Dynamically configure map sizes

Make the userspace agent set the BPF map sizes based on configured
options. This allows more suitable map sizes to be used during run
time than the static limits set in the BPF programs. This avoids
wasting memory by using unnecessary large maps, and might slightly
improve hashmap lookup performance by sizing them based on the
expected number of entries (small enough that many entries may fit in
cache, large enough to avoid excessive hash collisions).

Scale the histogram map based on the expected number of histograms,
the PID and ifindex filter maps to fit the largest key they need to
include and the cgroup filter map to fit all tracked cgroups.

This also fixes a bug where the maximum allowed PID (PID_MAX_LIMIT)
and ifindex (IFINDEX_MAX) did not fit in their corresponding filter
maps (off-by-one error).

Signed-off-by: Simon Sundberg <[email protected]>

Author: simosund

netstacklat/netstacklat.c

@@ -1012,9 +1012,15 @@ static int report_stats(const struct netstacklat_bpf *obj,
 	return 0;
 }
 
-static int init_histogram_buffer(struct histogram_buffer *buf)
+static int init_histogram_buffer(struct histogram_buffer *buf,
+				 const struct netstacklat_config *conf)
 {
-	int max_hists = NETSTACKLAT_N_HOOKS;
+	int max_hists = 0, i;
+
+	for (i = 0; i < NETSTACKLAT_N_HOOKS; i++) {
+		if (conf->enabled_hooks[i])
+			max_hists++;
+	}
 
 	buf->hists = calloc(max_hists, sizeof(*buf->hists));
 	if (!buf->hists)
@@ -1077,6 +1083,59 @@ static void set_programs_to_load(const struct netstacklat_config *conf,
 	}
 }
 
+static int set_map_sizes(const struct netstacklat_config *conf,
+			 struct netstacklat_bpf *obj, int max_hists)
+{
+	__u32 size;
+	int err, i;
+
+	size = max_hists * HIST_NBUCKETS;
+	err = bpf_map__set_max_entries(obj->maps.netstack_latency_seconds,
+				       size);
+	if (err) {
+		fprintf(stderr, "Failed setting size of histogram map to %u\n",
+			size);
+		return err;
+	}
+
+	// PID filter - arraymap, needs max PID + 1 entries
+	for (i = 0, size = 1; i < conf->npids; i++) {
+		if (conf->pids[i] >= size)
+			size = conf->pids[i] + 1;
+	}
+	err = bpf_map__set_max_entries(obj->maps.netstack_pidfilter, size);
+	if (err) {
+		fprintf(stderr, "Failed setting size of PID filter map to %u\n",
+			size);
+		return err;
+	}
+
+	// ifindex filter - arraymap, needs max ifindex + 1 entries
+	for (i = 0, size = 1; i < conf->nifindices; i++) {
+		if (conf->ifindices[i] >= size)
+			size = conf->ifindices[i] + 1;
+	}
+	err = bpf_map__set_max_entries(obj->maps.netstack_ifindexfilter, size);
+	if (err) {
+		fprintf(stderr,
+			"Failed setting size of ifindex filter map to %u\n",
+			size);
+		return err;
+	}
+
+	// cgroup filter - hashmap, should be ~2x expected number of entries
+	size = conf->bpf_conf.filter_cgroup ? conf->ncgroups * 2 : 1;
+	err = bpf_map__set_max_entries(obj->maps.netstack_cgroupfilter, size);
+	if (err) {
+		fprintf(stderr,
+			"Failed setting size of cgroup filter map to %u\n",
+			size);
+		return err;
+	}
+
+	return 0;
+}
+
 static int init_filtermap(int map_fd, void *keys, size_t nelem,
 			  size_t elem_size)
 {
@@ -1272,7 +1331,7 @@ int main(int argc, char *argv[])
 		return EXIT_FAILURE;
 	}
 
-	err = init_histogram_buffer(&hist_buf);
+	err = init_histogram_buffer(&hist_buf, &config);
 	if (err) {
 		fprintf(stderr, "Failed allocating buffer for histograms: %s\n",
 			strerror(-err));
@@ -1290,7 +1349,7 @@ int main(int argc, char *argv[])
 
 	obj = netstacklat_bpf__open();
 	if (!obj) {
-		err = libbpf_get_error(obj);
+		err = -errno;
 		libbpf_strerror(err, errmsg, sizeof(errmsg));
 		fprintf(stderr, "Failed opening eBPF object file: %s\n", errmsg);
 		goto exit_sockfd;
@@ -1301,6 +1360,13 @@ int main(int argc, char *argv[])
 
 	set_programs_to_load(&config, obj);
 
+	err = set_map_sizes(&config, obj, hist_buf.max_size);
+	if (err) {
+		libbpf_strerror(err, errmsg, sizeof(errmsg));
+		fprintf(stderr, "Failed configuring map sizes: %s\n", errmsg);
+		goto exit_destroy_bpf;
+	}
+
 	err = netstacklat_bpf__load(obj);
 	if (err) {
 		libbpf_strerror(err, errmsg, sizeof(errmsg));