program: add RecursionMisses to access ProgramInfo recursion misses counter

RecursionMisses is increased by one whenever a program is not executed due to recursion.

This value is always measured on supported kernels, regardless of
statistics being enabled or not.

Signed-off-by: Lorenz Bauer <[email protected]>
Signed-off-by: Jiri Olsa <[email protected]>

Author: olsajiri

info.go

@@ -83,6 +83,9 @@ type programStats struct {
 	runtime time.Duration
 	// Total number of times the program was called.
 	runCount uint64
+	// Total number of times the programm was NOT called.
+	// Added in commit 9ed9e9ba2337 ("bpf: Count the number of times recursion was prevented").
+	recursionMisses uint64
 }
 
 // ProgramInfo describes a program.
@@ -125,8 +128,9 @@ func newProgramInfoFromFd(fd *sys.FD) (*ProgramInfo, error) {
 		Name: unix.ByteSliceToString(info.Name[:]),
 		btf:  btf.ID(info.BtfId),
 		stats: &programStats{
-			runtime:  time.Duration(info.RunTimeNs),
-			runCount: info.RunCnt,
+			runtime:         time.Duration(info.RunTimeNs),
+			runCount:        info.RunCnt,
+			recursionMisses: info.RecursionMisses,
 		},
 	}
 
@@ -259,6 +263,16 @@ func (pi *ProgramInfo) Runtime() (time.Duration, bool) {
 	return time.Duration(0), false
 }
 
+// RecursionMisses returns the total number of times the program was NOT called.
+// This can happen when another bpf program is already running on the cpu, which
+// is likely to happen for example when you interrupt bpf program execution.
+func (pi *ProgramInfo) RecursionMisses() (uint64, bool) {
+	if pi.stats != nil {
+		return pi.stats.recursionMisses, true
+	}
+	return 0, false
+}
+
 // Instructions returns the 'xlated' instruction stream of the program
 // after it has been verified and rewritten by the kernel. These instructions
 // cannot be loaded back into the kernel as-is, this is mainly used for

info_test.go

@@ -262,6 +262,14 @@ func TestStats(t *testing.T) {
 		t.Errorf("expected a runtime of 0ns but got %v", rt)
 	}
 
+	rm, ok := pi.RecursionMisses()
+	if !ok {
+		t.Errorf("expected recursion misses info to be available")
+	}
+	if rm != 0 {
+		t.Errorf("expected a recursion misses of 0 but got %v", rm)
+	}
+
 	if err := testStats(prog); err != nil {
 		t.Error(err)
 	}