On Mon, Feb 13, 2017 at 05:24:36PM -0500, Waiman Long wrote: > >> movsql %edi, %rax; > >> movq __per_cpu_offset(,%rax,8), %rax; > >> cmpb $0, %[offset](%rax); > >> setne %al; > I have thought of that too. However, the goal is to eliminate memory > read/write from/to stack. Eliminating a register sign-extend instruction > won't help much in term of performance. Problem here is that all instructions have dependencies, so if you can get rid of the sign extend mov you kill a bunch of stall cycles (I would expect). But yes, peanuts vs the stack load/stores.
