calloc = malloc + memset

[Andi Kleen]

Marc Glisse <marc.glisse@inria.fr> writes:

> Hello,
>
> this is a stage 1 patch, and I'll ping it then, but if you have
> comments now...

FWIW i believe the transformation will break a large variety of micro benchmarks.

calloc internally knows that memory fresh from the OS is zeroed.
But the memory may not be faulted in yet.

memset always faults in the memory.

So if you have some test like

   buf = malloc(...)
   memset(buf, ...) 
   start = get_time();
   ... do something with buf
   end = get_time()

Now the times will be completely off because the measured times includes
the page faults.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only