操作系统：Ubuntu 14.04
CPU：i7
1.我安装了PyPy+Numpy：

sudo add-apt-repository ppa:pypy/ppa
sudo apt-get update
sudo apt-get install pypy pypy-dev
pip install git+https://bitbucket.org/pypy/numpy.git

1.使用python和pypy运行以下代码：

import numpy as np
import time

start = time.clock()

for i in range(5):
    vv = np.random.rand(9000000).astype(np.float32)
    m = np.mean(vv)

print 'Done in %.3f s %s ' % (time.clock()-start,m)

并获得了以下时间安排：

$python testSpeed_.py
Done in 1.908 s 0.499997

$pypy testSpeed_.py
Done in 4.599 s 0.499952167273

即没有性能改进。我应该得到性能提升吗？