libbpf-tools/softirqs: Add -c/--cpu option to filter cpu

tools/softirqs.py supports `-c/--cpu` otption to filter cpu,
It's reasonable to support a same otption for libbpf-tools/softirqs.

Reported-by: Tang Yizhou <tangyeechou@gmail.com>
Signed-off-by: Dantezy <zhangyet@gmail.com>

libbpf-tools/softirqs.bpf.c

@@ -9,6 +9,7 @@
 
 const volatile bool targ_dist = false;
 const volatile bool targ_ns = false;
+const volatile int targ_cpu = -1;
 
 struct {
  __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
@@ -21,8 +22,18 @@ __u64 counts[NR_SOFTIRQS] = {};
 __u64 time[NR_SOFTIRQS] = {};
 struct hist hists[NR_SOFTIRQS] = {};
 
+static bool is_target_cpu() {
+ if (targ_cpu < 0)
+ return true;
+
+ return bpf_get_smp_processor_id() == (u32)targ_cpu;
+}
+
 static int handle_entry(unsigned int vec_nr)
 {
+ if (!is_target_cpu())
+ return 0;
+
  u64 ts = bpf_ktime_get_ns();
  u32 key = 0;
 
@@ -32,11 +43,14 @@ static int handle_entry(unsigned int vec_nr)
 
 static int handle_exit(unsigned int vec_nr)
 {
+ if (!is_target_cpu())
+ return 0;
+
  u64 delta, *tsp;
  u32 key = 0;
 
- if (vec_nr >= NR_SOFTIRQS)
- return 0;
+ vec_nr &= 0xf; // to avoid compiler opti make verifier error
+
  tsp = bpf_map_lookup_elem(&start, &key);
  if (!tsp)
  return 0;

libbpf-tools/softirqs.c

@@ -24,10 +24,12 @@ struct env {
  int times;
  bool timestamp;
  bool verbose;
+ int targ_cpu;
 } env = {
  .interval = 99999999,
  .times = 99999999,
  .count = false,
+ .targ_cpu = -1,
 };
 
 static volatile bool exiting;
@@ -43,6 +45,7 @@ const char argp_program_doc[] =
 "EXAMPLES:\n"
 " softirqs # sum soft irq event time\n"
 " softirqs -d # show soft irq event time as histograms\n"
+" softirqs -c 1 # show soft irq event time on cpu 1\n"
 " softirqs 1 10 # print 1 second summaries, 10 times\n"
 " softirqs -NT 1 # 1s summaries, nanoseconds, and timestamps\n";
 
@@ -51,6 +54,7 @@ static const struct argp_option opts[] = {
  { "timestamp", 'T', NULL, 0, "Include timestamp on output", 0 },
  { "nanoseconds", 'N', NULL, 0, "Output in nanoseconds", 0 },
  { "count", 'C', NULL, 0, "Show event counts with timing", 0 },
+ {"cpu", 'c', "CPU", 0, "Trace this cpu only", 0},
  { "verbose", 'v', NULL, 0, "Verbose debug output", 0 },
  { NULL, 'h', NULL, OPTION_HIDDEN, "Show the full help", 0 },
  {},
@@ -79,6 +83,15 @@ static error_t parse_arg(int key, char *arg, struct argp_state *state)
  case 'C':
  env.count = true;
  break;
+ case 'c':
+ errno = 0;
+ long c = strtol(arg, NULL, 10);
+ if (errno || c < 0) {
+ fprintf(stderr, "invalid cpu: %s\n", arg);
+ argp_usage(state);
+ }
+ env.targ_cpu = (int)c;
+ break;
  case ARGP_KEY_ARG:
  errno = 0;
  if (pos_args == 0) {
@@ -228,6 +241,7 @@ int main(int argc, char **argv)
  /* initialize global data (filtering options) */
  obj->rodata->targ_dist = env.distributed;
  obj->rodata->targ_ns = env.nanoseconds;
+ obj->rodata->targ_cpu = env.targ_cpu;
 
  err = softirqs_bpf__load(obj);
  if (err) {