Performance Regression in Mongo-perf Commands.DistinctWithIndexAndQuery

python benchrun.py -t 8 -f testcases/*.js --includeFilter Commands.DistinctWithIndexAndQuery --out perf.json

pre = function( collection ) {

            collection.drop();

            var docs = [];

            for ( var i = 0; i < 4800; i++ ) {

                docs.push( { x : 1 } );

                docs.push( { x : 2 } );

                docs.push( { x : 3 } );

            }

            collection.insert(docs);

            collection.ensureIndex( { x : 1 } );

        };

use test0

pre(db.test)

benchRun({"ops":[{"op":"command","tags":["distinct","command","core"],"ns":"test0","command":{"distinct":"Commands_DistinctWithIndexAndQuery0","key":"x","query":{"x":1}},"safe":false,"w":0,"j":false,"writeCmd":true}],"seconds":5,"host":"127.0.0.1:27017","parallel":8})