fix perf test (facebookresearch#3253)

Summary:
Pull Request resolved: facebookresearch#3253

relaxing thresholds + allow equal, duh

Reviewed By: mlomeli1

Differential Revision: D53803000

fbshipit-source-id: 7b68386523d9a44a0cd8e099fc1d72b3ed7d5e43

Author: algoriddle

tests/test_fastscan_perf.cpp

@@ -64,7 +64,7 @@ TEST(TestFastScan, knnVSrange) {
                               .count();
 
     // we expect the perf of knn and range search
-    // to be similar, at least within a factor of 2
-    ASSERT_LT(range_time, knn_time * 2);
-    ASSERT_LT(knn_time, range_time * 2);
+    // to be similar, at least within a factor of 4
+    ASSERT_LE(range_time, knn_time * 4);
+    ASSERT_LE(knn_time, range_time * 4);
 }