[#14] mclock: Allow to prohibit tag requests

It is now possible to restrict requests for a specific tag.
A separate field in `TagInfo` is used to avoid comparing float64 values with zero.

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

scheduling/mclock.go

@@ -22,6 +22,7 @@ var (
 	ErrMClockSchedulerUnknownTag           = errors.New("unknown tag")
 	ErrInvalidTagInfo                      = errors.New("invalid tag info: shares, limit and reservation must be greater than zero")
 	ErrInvalidRunLimit                     = errors.New("invalid run limit: must be greater than zero")
+	ErrTagRequestsProhibited               = errors.New("tag requests are prohibited")
 )
 
 type request struct {
@@ -49,6 +50,7 @@ type TagInfo struct {
 	ReservedIOPS *float64
 	LimitIOPS    *float64
 	Share        float64
+	Prohibited   bool
 }
 
 // MClock is mClock scheduling algorithm implementation.
@@ -196,6 +198,9 @@ func (q *MClock) pushRequest(tag string) (*request, ReleaseFunc, error) {
 	if !ok {
 		return nil, nil, ErrMClockSchedulerUnknownTag
 	}
+	if tagInfo.Prohibited {
+		return nil, nil, ErrTagRequestsProhibited
+	}
 	prev, ok := q.previous[tag]
 	assert.Cond(ok, "undefined previous:", tag)
 

scheduling/mclock_test.go

@@ -563,3 +563,22 @@ func TestMClockLimitTotalTime(t *testing.T) {
 	require.True(t, time.Since(startedAt) >= 1500*time.Millisecond)
 	require.True(t, time.Since(startedAt) <= 1600*time.Millisecond) // 100 ms offset to complete all requests
 }
+
+func TestMClockRestictTagRequests(t *testing.T) {
+	t.Parallel()
+	limit := 10.0
+	q, err := NewMClock(100, 100, map[string]TagInfo{
+		"class1": {Share: 50, LimitIOPS: &limit},
+		"class2": {Share: 50, LimitIOPS: &limit, Prohibited: true},
+	}, 5*time.Second)
+	require.NoError(t, err)
+	defer q.Close()
+
+	release, err := q.RequestArrival(context.Background(), "class1")
+	require.NoError(t, err)
+	release()
+
+	release, err = q.RequestArrival(context.Background(), "class2")
+	require.ErrorIs(t, err, ErrTagRequestsProhibited)
+	require.Nil(t, release)
+}