BenchmarkAggregate: also test with 2 input series, and test using Min

so that we can better see the effect of
#1164

Author: Dieterbe

expr/func_aggregate_test.go

@@ -272,6 +272,9 @@ func testAggregate(name, agg string, in [][]models.Series, out models.Series, t
 func BenchmarkAggregate10k_1NoNulls(b *testing.B) {
 	benchmarkAggregate(b, 1, test.RandFloats10k, test.RandFloats10k)
 }
+func BenchmarkAggregate10k_2NoNulls(b *testing.B) {
+	benchmarkAggregate(b, 2, test.RandFloats10k, test.RandFloats10k)
+}
 func BenchmarkAggregate10k_10NoNulls(b *testing.B) {
 	benchmarkAggregate(b, 10, test.RandFloats10k, test.RandFloats10k)
 }
@@ -285,6 +288,9 @@ func BenchmarkAggregate10k_1000NoNulls(b *testing.B) {
 func BenchmarkAggregate10k_1SomeSeriesHalfNulls(b *testing.B) {
 	benchmarkAggregate(b, 1, test.RandFloats10k, test.RandFloatsWithNulls10k)
 }
+func BenchmarkAggregate10k_2SomeSeriesHalfNulls(b *testing.B) {
+	benchmarkAggregate(b, 2, test.RandFloats10k, test.RandFloatsWithNulls10k)
+}
 func BenchmarkAggregate10k_10SomeSeriesHalfNulls(b *testing.B) {
 	benchmarkAggregate(b, 10, test.RandFloats10k, test.RandFloatsWithNulls10k)
 }
@@ -298,6 +304,9 @@ func BenchmarkAggregate10k_1000SomeSeriesHalfNulls(b *testing.B) {
 func BenchmarkAggregate10k_1AllSeriesHalfNulls(b *testing.B) {
 	benchmarkAggregate(b, 1, test.RandFloatsWithNulls10k, test.RandFloatsWithNulls10k)
 }
+func BenchmarkAggregate10k_2AllSeriesHalfNulls(b *testing.B) {
+	benchmarkAggregate(b, 2, test.RandFloatsWithNulls10k, test.RandFloatsWithNulls10k)
+}
 func BenchmarkAggregate10k_10AllSeriesHalfNulls(b *testing.B) {
 	benchmarkAggregate(b, 10, test.RandFloatsWithNulls10k, test.RandFloatsWithNulls10k)
 }
@@ -324,7 +333,7 @@ func benchmarkAggregate(b *testing.B, numSeries int, fn0, fn1 func() []schema.Po
 	b.ResetTimer()
 	var err error
 	for i := 0; i < b.N; i++ {
-		f := NewAggregateConstructor("average", crossSeriesAvg)()
+		f := NewAggregateConstructor("min", crossSeriesMin)()
 		avg := f.(*FuncAggregate)
 		avg.in = append(avg.in, NewMock(input))
 		results, err = f.Exec(make(map[Req][]models.Series))