Module vs Kernel main performacne

[Abu Rasheda]

I did another experiment.

Wrote a stand alone module and user program which does ioctl and pass
buffer to kernel module.

User program passes a buffer through ioctl and kernel module does
kmalloc on it and calls copy_from_user, kfree and return. Test program
send 120 gigabyte data to module.

If I pass 1k buffer per call, I get

115,396,349,819 instructions              #    0.90  insns per cycle
      [95.00%]

as I increase size of buffer, insns per cycle keep decreasing. Here is the data:

    1k 0.90  insns per cycle
    8k 0.43  insns per cycle
  43k 0.18  insns per cycle
100k 0.08  insns per cycle

Showing that cop_from_user is more efficient when copy data is small,
why it is so ?