On Mon, Jun 23, 2014 at 09:00:02PM +0200, Marc Glisse wrote: > On Mon, 23 Jun 2014, Andi Kleen wrote: > > >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. > > Good point. I guess working around compiler optimizations is part of > the game for micro benchmarks, and their authors would be > disappointed if the compiler didn't mess it up regularly in new and > entertaining ways ;-)
I would prefer to not do it. I'm not sure it has a lot of benefit. If you want to keep it please make sure there is an easy way to turn it off. -Andi -- a...@linux.intel.com -- Speaking for myself only.
