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-Function- >> >> >> > > 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/
