On Fri, 2012-04-27 at 14:46 -0400, Steven Rostedt wrote: > Currently, function tracing selects CONFIG_FRAME_POINTER for various > archs (including x86), as the kernel will not compile without it, if > function tracing is enabled. But if -mfentry is available with the > compiler, it does not have this dependency. The kernel will compile fine > with -pg -mfentry and without frame pointers. Just to show the difference. I ran several iterations of hackbench, on an Intel Quad Core2 2.6GHz. Here's the fentry code with frame pointers (tracing disabled): Time: 2.006 Time: 2.028 Time: 2.028 Time: 1.999 Time: 2.035 Time: 2.037 Time: 2.006 Time: 1.996 Time: 2.049 Time: 1.991 Time: 2.038 Time: 2.047 Time: 2.039 Time: 2.000 Time: 2.021 Time: 2.011 Time: 2.007 Time: 2.024 Time: 2.033 Time: 2.027 Time: 2.044 And the fentry code with frame pointers disabled: Time: 1.870 Time: 1.861 Time: 1.865 Time: 1.884 Time: 1.867 Time: 1.867 Time: 1.875 Time: 1.883 Time: 1.863 Time: 1.877 Time: 1.865 Time: 1.885 Time: 1.842 Time: 1.863 Time: 1.899 Time: 1.877 Time: 1.837 Time: 1.900 Time: 1.897 Time: 1.877 Time: 1.853 Time: 1.856 That's about a 8% difference. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
