Hi Victor, Ah! That looks pretty cool. I'll have to try it out on Open vSwitch. I don't know if I'll get the chance to use it right away but when I do I'll let you know how I got on. Thanks, Billy. > -----Original Message----- > From: Victor Rodriguez [mailto:vm.rod25@xxxxxxxxx] > Sent: Monday, April 10, 2017 10:43 PM > To: O Mahony, Billy <billy.o.mahony@xxxxxxxxx> > Cc: Evgeny Stupachenko <evstupac@xxxxxxxxx>; Xi Ruoyao > <ryxi@xxxxxxxxxxxxxxxxx>; gcc-help@xxxxxxxxxxx > Subject: Re: Function Multiversioning in GCC6 > > On Thu, Apr 6, 2017 at 5:04 AM, O Mahony, Billy <billy.o.mahony@xxxxxxxxx> > wrote: > > > > > >> -----Original Message----- > >> From: Victor Rodriguez [mailto:vm.rod25@xxxxxxxxx] > >> Sent: Wednesday, April 5, 2017 8:09 PM > >> To: O Mahony, Billy <billy.o.mahony@xxxxxxxxx>; Evgeny Stupachenko > >> <evstupac@xxxxxxxxx> > >> Cc: Xi Ruoyao <ryxi@xxxxxxxxxxxxxxxxx>; gcc-help@xxxxxxxxxxx > >> Subject: Re: Function Multiversioning in GCC6 > >> > >> On Tue, Apr 4, 2017 at 4:18 AM, O Mahony, Billy > >> <billy.o.mahony@xxxxxxxxx> > >> wrote: > >> > Hi Victor, > >> > > >> >> -----Original Message----- > >> >> From: Victor Rodriguez [mailto:vm.rod25@xxxxxxxxx] > >> >> Sent: Monday, April 3, 2017 10:29 PM > >> >> To: O Mahony, Billy <billy.o.mahony@xxxxxxxxx> > >> >> Cc: Xi Ruoyao <ryxi@xxxxxxxxxxxxxxxxx>; gcc-help@xxxxxxxxxxx > >> >> Subject: Re: Function Multiversioning in GCC6 > >> >> > >> >> On Thu, Mar 30, 2017 at 3:59 AM, O Mahony, Billy > >> >> <billy.o.mahony@xxxxxxxxx> wrote: > >> >> > Hi Victor, > >> >> > > >> >> > Thanks to you and Abraham Duenas, and Evgeny Stupachenko for > >> >> > your > >> >> work on FMV - it's a very neat feature and from my own > >> >> investigations so far it works with minimal overhead even when > >> >> used with inlined > >> functions. > >> >> > > >> >> Welcome :) > >> >> > >> >> > One thing that could be stated explicitly in the article is that > >> >> > use of the 'target' attribute with identically named functions > >> >> > (i.e. the first code sample in the lwn article) is still > >> >> > C++-only in gcc-6 > >> >> > >> >> yes > >> >> > >> >> and if you want to do this with C you need to create your own > >> >> ifunc resolver and have several differently named functions. > >> >> > > >> >> > >> >> The idea is that you use one single funtion with just atributes , > >> >> instead of multiple funtions > >> >> > >> >> Why do you need old implementation of C++ FMV in C ? > >> > > >> > [[BO'M]] > >> > I'm working on a code base that already has different definitions > >> > of > >> functions optimized for specific cpu instruction sets. One definition > >> is picked by macro at compile time based on make flags. > >> > > >> Sounds interesting, If something is not optimized for particular > >> target you should file a bugzilla report. if is proper for your > >> code, then as you mention FMV is not the best option. However try to > >> reevaluate if this is the best approach for your application. Maybe > >> is a good time to rewrite it and make more compact and understandable. > >> > >> > In my experiments with FMV I've looked at a hashing function. There > >> > are > >> two definitions - a pure C definition and one that uses sse42 > >> intrinsics. The pure C impl is really a set of inlined functions as I > >> pulled it out of a suite of hashing functions (hash32, hash64, > >> hash32_array, etc etc) for the purposes of the experiment. > >> > > >> > I'm assuming that, sophisticated as compilers are now, it won't > >> > replace the > >> several layers of inlined C functions with single sse42 intrinsic > >> call just because I specify "sse42" as one of the list of > >> target_clones. So I stuck with the several definitions solution. > >> > >> Is your code open source ? so we can tak ea look ? > > [[BO'M]] Hi Victor, > > I'm looking at this wrt to Open vSwitch code > > https://github.com/openvswitch/ovs > > > > As an experiment I was compiling a test program with both the sse42 and > default versions of hash_words_inline function which are both in lib/hash.h. > Currently one implementation or the other is chosen by compile time #def. > > > You can use our code to generate the FMV patch: > > https://github.com/clearlinux/make-fmv-patch > > You just need to build with -fopt-info-vec > > The idea is to generate the patch automatically and then you can choose > which patch to apply based on the functions you consider relevant for FMV > > > It looks like ifunc is supported by the latest version of clang. Do you know if > it is supported by BSD and Windows. > > it is not as far as I know > > Hope it helps > > Regards > Victor > > > > > Thanks, > > Billy. > > > >> > >> > > >> > > >> >> > >> >> Regards > >> >> > >> >> > Thanks, > >> >> > Billy. > >> >> > > >> >> > > >> >> > > >> >> >> -----Original Message----- > >> >> >> From: Victor Rodriguez [mailto:vm.rod25@xxxxxxxxx] > >> >> >> Sent: Thursday, March 30, 2017 1:10 AM > >> >> >> To: O Mahony, Billy <billy.o.mahony@xxxxxxxxx> > >> >> >> Cc: Xi Ruoyao <ryxi@xxxxxxxxxxxxxxxxx>; gcc-help@xxxxxxxxxxx > >> >> >> Subject: Re: Function Multiversioning in GCC6 > >> >> >> > >> >> >> On Thu, Mar 23, 2017 at 4:45 AM, O Mahony, Billy > >> >> >> <billy.o.mahony@xxxxxxxxx> wrote: > >> >> >> > > >> >> >> > Hi Xi, > >> >> >> > > >> >> >> > Thanks for the clarification/confirmation. > >> >> >> > > >> >> >> > Regards, > >> >> >> > Billy. > >> >> >> > > >> >> >> > > -----Original Message----- > >> >> >> > > From: Xi Ruoyao [mailto:ryxi@xxxxxxxxxxxxxxxxx] > >> >> >> > > Sent: Thursday, March 23, 2017 9:21 AM > >> >> >> > > To: O Mahony, Billy <billy.o.mahony@xxxxxxxxx> > >> >> >> > > Cc: ryxi@xxxxxxxxxxxxxxxxx; gcc-help@xxxxxxxxxxx > >> >> >> > > Subject: Re: Function Multiversioning in GCC6 > >> >> >> > > > >> >> >> > > On 2017-03-22 10:51 +0000, O Mahony, Billy wrote: > >> >> >> > > > >> >> >> > > > However when I compile the first example in this LWN > >> >> >> > > > article https://lwn.net/Articles/691932/ with gcc-6 C > >> >> >> > > > compiler it fails with > >> >> >> > > > (error: redefinition of > >> >> >> > > > 'foo'...) . > >> >> >> > > > >> >> >> > > The document > >> >> >> > > <https://gcc.gnu.org/onlinedocs/gcc-6.3.0/gcc/Function- > >> >> >> > > Multiversioning.html> said: > >> >> >> > > > >> >> >> > > With the GNU *C++* front end, for x86 targets, you may > >> >> >> > > specify multiple versions of the function. > >> >> >> > > > >> >> >> > > FMV doesn't work with C FE. In C, > >> >> >> > > __attribute__((target("sse4.2"))) just means to compile > >> >> >> > > this function with -msse4.2, see > >> >> >> > > <https://gcc.gnu.org/onlinedocs/gcc-6.3.0/gcc/Common-Functi > >> >> >> > > on- > >> >> >> > > Attributes.html>. > >> >> >> > > > >> >> >> > > -- > >> >> >> > > Xi Ruoyao <ryxi@xxxxxxxxxxxxxxxxx> School of Aerospace > >> >> >> > > Science and Technology, Xidian University > >> >> >> > > >> >> >> > >> >> >> You can also read this LWN article: > >> >> >> > >> >> >> https://lwn.net/Articles/691932/
