Optimize mathematical library (libm)

Question

Have anyone tried to compile glibc with -march=corei7 to see if there's any performance improvement over the version that comes by default with any Linux x68_64 distribution? GCC is compiled with -march=i686. I think (not sure) that the mathematical library is also compiled the same way. Can anybody confirm this?

Answer 1

Most Linux distributions for x86 compile using only i686 instructions, but asking for scheduling them for later processors. I haven't really followed later developments.

A long while back different versions of system libraries according to processor lines were common, but the performance differences were soon deemed too small for the cost. And machines got more uniform in performance meanwhile.

One thing that has to be remembered always is that today's machines are memory bound. I.e., today a memory access takes a few hundred times longer than an instruction, and the gap is growing. Not to mention that this machine (an oldish laptop, was top-of-the-line some 2 years back) has 4 cores (8 threads), all battling to get data/instructions from memory. Making the code run a tiny bit faster, so the CPU can wait longer for RAM, isn't very productive.