using get_cycles() to get the real elapsed time

[Li Guanglei <guanglei at cn dot ibm dot com>]

Hi,
  I took a look at the runtime/time.c and found it uses 
get_cycles()/freq to get the elapsed time:

   ...
   delta = get_cycles() - last;
   do_div(delta, freq);
   ...
   return (USEC_PER_SEC * (int64_t)base.tv_sec) + base.tv_usec + delta;

  But AFAIK, some architectures will increase Time Base register(i.e 
TSC) with a fixed ratio of cpu freq. On x86, this = cpu freq. and on 
Power5, Time Base driven at 1/8 the processor clock frequency. I even 
remembered that on some old PowerPC(4xx, 7xx) the Time Base is driven 
by the bus clock(33Mhz)

 So we need deal with different Arches to get the elapsed time by 
using get_cycles()

 BTW, get_cycles() will return 32-bit value for some architectures 
e.g ppc32, although the major architectures such as ppc64, x86, x86_64 
will all return a 64-bit value. Should we care about those 
architectures whose get_cycles() returns 32-bit value?

 Thanks.

- Guanglei