On Sat, Jan 10, 2015 at 10:02 PM, Andy Lutomirski <l...@amacapital.net> wrote: > On Sat, Jan 10, 2015 at 12:42 PM, Borislav Petkov <b...@alien8.de> wrote: >> On Sat, Jan 10, 2015 at 12:17:13PM -0800, Andy Lutomirski wrote: >>> I asked this once, and someone told me that push/pop has lower >>> throughput. I find this surprising. >> >> Implicit dependency on %rsp probably. The MOVs allow you to start more >> stuff out-of-order I'd guess... > > AIUI modern CPUs have fancy stack engines that match call/ret pairs, > and presumably they can speculate rsp values across multiple pushes > and pops very quickly.
Yes, stack engine hangs off the pipeline right after decode stage. > Also, don't compilers generally use push and pop to save and restore > callee-saved registers? I think that function calls are common enough > that the CPU vendors would have made these sequences fast. Compilers can't predict which functions are hottest. Using mov's would bloat prologues by about factor of 5. I think using push/pop is okay. In the very hottest code paths you may want to prefer mov's. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/