On Thu, Dec 4, 2014 at 10:05 AM, Joe Perches <[email protected]> wrote: > On Thu, 2014-12-04 at 07:56 -0800, Alexei Starovoitov wrote: >> On Thu, Dec 4, 2014 at 1:26 AM, Joe Perches <[email protected]> wrote: >> > On Thu, 2014-11-27 at 10:49 -0800, Joe Perches wrote: >> >> On Thu, 2014-11-27 at 12:25 +0000, David Laight wrote: >> >> > Why the change in data? >> >> >> >> btw: without gcov and using -O2 >> >> >> >> $ size arch/x86/net/bpf_jit_comp.o* >> >> text data bss dec hex filename >> >> 9671 4 0 9675 25cb >> >> arch/x86/net/bpf_jit_comp.o.new >> >> 10679 4 0 10683 29bb >> >> arch/x86/net/bpf_jit_comp.o.old >> > >> > Alexei? >> > >> > Is this 10% reduction in size a good reason to change the code? >> >> yes. >> I believe you're seeing it with gcc 4.9. I wanted to double >> check what 4.6 and 4.7 are doing. If they're not suddenly >> increase code size then resubmit it for inclusion please. > > I get these sizes for these compilers > (x86-64, -O2, without profiling) > > $ size arch/x86/net/bpf_jit_comp.o* > text data bss dec hex filename > 9266 4 0 9270 2436 arch/x86/net/bpf_jit_comp.o.4.4.new > 10042 4 0 10046 273e arch/x86/net/bpf_jit_comp.o.4.4.old > 9109 4 0 9113 2399 arch/x86/net/bpf_jit_comp.o.4.6.new > 9717 4 0 9721 25f9 arch/x86/net/bpf_jit_comp.o.4.6.old > 8789 4 0 8793 2259 arch/x86/net/bpf_jit_comp.o.4.7.new > 10245 4 0 10249 2809 arch/x86/net/bpf_jit_comp.o.4.7.old > 9671 4 0 9675 25cb arch/x86/net/bpf_jit_comp.o.4.9.new > 10679 4 0 10683 29bb arch/x86/net/bpf_jit_comp.o.4.9.old > > I am a bit surprised by the size variations
yeah. the difference is surprising. Just tried with 4.7 and my regular config and I see the same difference. Looks like gcc wasn't able to fold conditions into cmov and used a bunch of cmp/jmp Since is_ereg() was inlined ~70 times on its own and as part of other functions, the difference of 3-4 instructions may a large difference in total size. test_bpf also passes, so please resubmit properly. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
