[Click] click performance test

[Jiangbo Li]

hi, Eddie Kohler,

I am doing performance test on click elements. I use RDTSC 
to read the performance counter.  In your thesis, you got the 
very accurate results like checkipheader takes 457ns/packet.
How can you get the result so accurate? 

Another problem is when I do two continuous RDTSC, It took 85
cycles. Seems to much. Is there anything I missed?

the following code is what I used to get the hardware clock:
 #define rdtsc(low,high) \
    __asm__ __volatile__("rdtsc" : "=a" (low), "=d" (high))

 register unsigned long low, high;
 rdtsc(low, high);


Thank you very much,

Jiangbo Li