Fix offwaketime PID / TGID handling

tools/offwaketime.py

@@ -114,58 +114,73 @@ def signal_ignore(signal, frame):
  int t_k_stack_id;
  int t_u_stack_id;
  u32 t_pid;
+ u32 t_tgid;
  u32 w_pid;
- u32 tgid;
+ u32 w_tgid;
 };
 BPF_HASH(counts, struct key_t);
+
+// Key of this hash is PID of waiting Process,
+// value is timestamp when it went into waiting
 BPF_HASH(start, u32);
+
 struct wokeby_t {
  char name[TASK_COMM_LEN];
  int k_stack_id;
  int u_stack_id;
  int w_pid;
+ int w_tgid;
 };
+// Key of the hash is PID of the Process to be waken, value is information
+// of the Process who wakes it
 BPF_HASH(wokeby, u32, struct wokeby_t);
 
 BPF_STACK_TRACE(stack_traces, STACK_STORAGE_SIZE);
 
 int waker(struct pt_regs *ctx, struct task_struct *p) {
+ // PID and TGID of the target Process to be waken
  u32 pid = p->pid;
  u32 tgid = p->tgid;
 
  if (!(THREAD_FILTER)) {
  return 0;
  }
 
+ // Construct information about current (the waker) Process
  struct wokeby_t woke = {};
  bpf_get_current_comm(&woke.name, sizeof(woke.name));
-
  woke.k_stack_id = KERNEL_STACK_GET;
  woke.u_stack_id = USER_STACK_GET;
- woke.w_pid = pid;
+ woke.w_pid = bpf_get_current_pid_tgid();
+ woke.w_tgid = bpf_get_current_pid_tgid() >> 32;
+
  wokeby.update(&pid, &woke);
  return 0;
 }
 
 int oncpu(struct pt_regs *ctx, struct task_struct *p) {
- u32 pid = p->pid, t_pid=pid;
+ // PID and TGID of the previous Process (Process going into waiting)
+ u32 pid = p->pid;
  u32 tgid = p->tgid;
- u64 ts, *tsp;
+ u64 *tsp;
+ u64 ts = bpf_ktime_get_ns();
 
- // record previous thread sleep time
+ // Record timestamp for the previous Process (Process going into waiting)
  if (THREAD_FILTER) {
- ts = bpf_ktime_get_ns();
  start.update(&pid, &ts);
  }
 
- // calculate current thread's delta time
+ // Calculate current Process's wait time by finding the timestamp of when
+ // it went into waiting.
+ // pid and tgid are now the PID and TGID of the current (waking) Process.
  pid = bpf_get_current_pid_tgid();
  tgid = bpf_get_current_pid_tgid() >> 32;
  tsp = start.lookup(&pid);
  if (tsp == 0) {
- return 0; // missed start or filtered
+ // Missed or filtered when the Process went into waiting
+ return 0;
  }
- u64 delta = bpf_ktime_get_ns() - *tsp;
+ u64 delta = ts - *tsp;
  start.delete(&pid);
  delta = delta / 1000;
  if ((delta < MINBLOCK_US) || (delta > MAXBLOCK_US)) {
@@ -176,18 +191,19 @@ def signal_ignore(signal, frame):
  u64 zero = 0, *val;
  struct key_t key = {};
  struct wokeby_t *woke;
- bpf_get_current_comm(&key.target, sizeof(key.target));
 
+ bpf_get_current_comm(&key.target, sizeof(key.target));
+ key.t_pid = pid;
+ key.t_tgid = tgid;
  key.t_k_stack_id = KERNEL_STACK_GET;
  key.t_u_stack_id = USER_STACK_GET;
- key.t_pid = t_pid;
 
  woke = wokeby.lookup(&pid);
  if (woke) {
  key.w_k_stack_id = woke->k_stack_id;
  key.w_u_stack_id = woke->u_stack_id;
  key.w_pid = woke->w_pid;
- key.tgid = tgid;
+ key.w_tgid = woke->w_tgid;
  __builtin_memcpy(&key.waker, woke->name, TASK_COMM_LEN);
  wokeby.delete(&pid);
  }
@@ -295,7 +311,7 @@ def signal_ignore(signal, frame):
  # print folded stack output
  line = \
  [k.target.decode()] + \
- [b.sym(addr, k.tgid)
+ [b.sym(addr, k.t_tgid)
  for addr in reversed(list(target_user_stack)[1:])] + \
  (["-"] if args.delimited else [""]) + \
  [b.ksym(addr)
@@ -304,7 +320,7 @@ def signal_ignore(signal, frame):
  [b.ksym(addr)
  for addr in reversed(list(waker_kernel_stack))] + \
  (["-"] if args.delimited else [""]) + \
- [b.sym(addr, k.tgid)
+ [b.sym(addr, k.w_tgid)
  for addr in reversed(list(waker_user_stack))] + \
  [k.waker.decode()]
  print("%s %d" % (";".join(line), v.value))
@@ -313,7 +329,7 @@ def signal_ignore(signal, frame):
  # print wakeup name then stack in reverse order
  print(" %-16s %s %s" % ("waker:", k.waker.decode(), k.t_pid))
  for addr in waker_user_stack:
- print(" %s" % b.sym(addr, k.tgid))
+ print(" %s" % b.sym(addr, k.w_tgid))
  if args.delimited:
  print(" -")
  for addr in waker_kernel_stack:
@@ -328,7 +344,7 @@ def signal_ignore(signal, frame):
  if args.delimited:
  print(" -")
  for addr in target_user_stack:
- print(" %s" % b.sym(addr, k.tgid))
+ print(" %s" % b.sym(addr, k.t_tgid))
  print(" %-16s %s %s" % ("target:", k.target.decode(), k.w_pid))
  print(" %d\n" % v.value)