问为什么ConcurrentSkipListSet升序迭代器比降序迭代器“快”？

EN

@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.MILLISECONDS)
@Warmup(iterations = 5, time = 5, timeUnit = TimeUnit.SECONDS)
@Measurement(iterations = 5, time = 5, timeUnit = TimeUnit.SECONDS)
@State(Scope.Thread)
public class ConcurrentSkipListSetIteratorTest {

    @Fork(1)
    @Benchmark
    public void ascItr(SetupParams params) {
        Iterator<Integer> itr = params.cslset.iterator();
        while (itr.hasNext()) itr.next();
    }

    @Fork(1)
    @Benchmark
    public void dscItr(SetupParams params) {
        Iterator<Integer> itr = params.cslset.descendingIterator();
        while (itr.hasNext()) itr.next();
    }

    @State(Scope.Benchmark)
    public static class SetupParams {

        private ConcurrentSkipListSet<Integer> cslset;

        @Setup(Level.Invocation)
        public void setUp() {
            cslset = new SplittableRandom()
                .ints(100_000, 0, 100_000)
                .boxed()
                .collect(Collectors.toCollection(ConcurrentSkipListSet::new));
        }
    }
}

public static void main(String[] args) throws RunnerException {
    Options opt = new OptionsBuilder()
        .include(ConcurrentSkipListSetIteratorTest.class.getSimpleName())
        .jvmArgs("-ea", "-Xms512m", "-Xmx1024m")
        .shouldFailOnError(true)
        .build();
    new Runner(opt).run();
}

private void ascend() {
    ...
    for (;;) {
        // there is a link to the next node
        next = next.next; // O(1) operation
        ...
    }
}

private void descend() {
    ...
    for (;;) {
        // but, there is no link to the previous node
        next = m.findNear(lastReturned.key, LT, cmp); // O(logN) operation
        ...
    }
}

Benchmark  Mode  Cnt  Score   Error  Units
ascItr     avgt    5  0,075 ± 0,029  ms/op
dscItr     avgt    5  0,810 ± 0,116  ms/op

Benchmark  Mode  Cnt   Score   Error  Units
ascItr     avgt    5   2,764 ± 1,160  ms/op
dscItr     avgt    5  11,110 ± 0,937  ms/op