On Fri, Feb 20, 2015 at 05:38:55PM -0800, Andi Kleen wrote: > This patch moves the MSR functions out of line. A MSR access is typically > 40-100 cycles or even slower, a call is a few cycles at best, so the > additional function call is not really significant.
If I look at the below PDF a CALL+PUSH EBP+MOV RSP,RBP+ ... +POP+RET ends up being 5+1.5+0.5+ .. + 1.5+8 = 16.5 + .. cycles. ~16 is fairly significant on 40. And I figure people are working hard to make some MSR accesses cheaper, which means it'll be even worse in the future. Now I appreciate the intent for debuggability, but I don't think we can do this unconditionally. http://www.intel.com/content/www/us/en/architecture-and-technology/64-ia-32-architectures-optimization-manual.html -- 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/
