> On Nov 23, 2015, at 5:08 PM, Ben Pfaff <b...@ovn.org> wrote: > > On Mon, Nov 23, 2015 at 04:26:18PM -0800, Joe Stringer wrote: >> On 23 November 2015 at 12:49, Joe Stringer <joestrin...@nicira.com> wrote: >>> On 23 November 2015 at 10:06, Ben Pfaff <b...@ovn.org> wrote: >>>> When Joe added these types I assumed that he used the unconventional >>>> prototypes for hton128() and ntoh128() because the return value >>>> convention was inefficient. If GCC and Clang actually optimize the use >>>> of a return value in some kind of sensible way then I agree that the >>>> usual convention is nicer. >>>> >>>> Joe, did you have another reason? >>> >>> This was mostly done based on an assumption that this was more >>> optimal, rather than actually digging into the compiled code and >>> seeing that it was generated differently. >>> >>> Looking now, before this patch vs. after on my 64-bit system.. >>> >>> GCC-4.9: hton128/ntoh128 require one less MOV with this patch, but >>> calling conventions (in format_u128) require 3 extra MOV (+4 MOV, -1 >>> LEA) for format_u128(). >>> Clang-3.7: hton128/ntoh128 are roughly equivalent, although with this >>> patch they use some MOVUPS/MOVAPS instructions for 128-bit moves. >>> Calling conventions seem to require as much as 6-12 (!) extra MOVs >>> however, details below. >> >> <snip> >> >> Woops, looks like I missed compiler optimizations. They look much >> closer together with --O2, so I think this patch makes sense to apply >> without reservation.
Thanks for the thorough analysis, Joe. > Acked-by: Ben Pfaff <b...@ovn.org> Thanks for the reviews, Ben. I'll push the series in a minute. --Justin _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
