On Wed, 2014-11-26 at 10:34 -0800, Alexei Starovoitov wrote: > On Wed, Nov 26, 2014 at 10:02 AM, Joe Perches <[email protected]> wrote: > > On Wed, 2014-11-26 at 09:23 -0800, Alexei Starovoitov wrote: > >> On Wed, Nov 26, 2014 at 8:58 AM, Joe Perches <[email protected]> wrote: > > > >> > Is there any value in reordering these tests for frequency > >> > or maybe using | instead of || to avoid multiple jumps? > >> > >> probably not. It's not a critical path. > >> compiler may fuse conditions depending on values anyway. > >> If it was a critical path, we could have used > >> (1 << reg) & mask trick. > >> I picked explicit 'return true' else 'return false' here, > >> because it felt easier to read. Just a matter of taste. > > > > There is a size difference though: (allyesconfig) > > > > $ size arch/x86/net/built-in.o* > > text data bss dec hex filename > > 12999 1012 4336 18347 47ab arch/x86/net/built-in.o.new > > 13177 1076 4592 18845 499d arch/x86/net/built-in.o.old > > interesting. Compiler obviously thinks that 178 byte increase > with -O2 is the right trade off. Which I agree with :)
498 overall. > If I think dropping 'inline' and using -Os will give bigger savings... > but I suspect 'tinification' folks will compile JIT out anyway... Smaller is generally better/faster in any case. > thanks for giving it a shot :) > That's exactly what I had in mind. > imo it's less readable, but we probably not going > to mess much with this piece of code anyway. > Though to be safe in the future, we'd need to > add BUILD_BUG_ON that largest value (AUX_REG) > fits in 32bit (or 64bit) and add a comment that > verifier goes before the JIT and checks that > insn->src_reg, insn->dst_reg are less than MAX_BPF_REG, > so argument 'reg' also doesn't trigger too large shift. > Perfectionists r us. :) > ... or just leave it as-is ;) 16 registers max anyway as it's stored in a :4 No worries, it was just playtime anyway. cheers, Joe -- 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/
