Date: Sun, 13 Jan 2013 15:00:11 -0800 From: Peter Wemm <peter@wemm.org> To: Nathan Whitehorn <nwhitehorn@freebsd.org> Cc: freebsd-arch@freebsd.org Subject: Re: how long to keep support for gcc on x86? Message-ID: <CAGE5yCq4k7-ko9WnAB5SvSMMHQZfuD2Hwb5Mqk1JRd3QOgr6pg@mail.gmail.com> In-Reply-To: <50F33B02.6040303@freebsd.org> References: <20130112233147.GK1410@funkthat.com> <20130113014242.GA61609@troutmask.apl.washington.edu> <CAJ-VmomrSFXcZg%2BKj6C2ARhpmjB9hxZATYJyRZB7-eRrcBLprg@mail.gmail.com> <20130113053725.GL1410@funkthat.com> <CAJ-VmomGKayr-1VucfwgodhXEHrXxx8r=9crHZJf74iVKZyTmQ@mail.gmail.com> <20130113202952.GO1410@funkthat.com> <CAGE5yCpB8dHLn0TaW=r0Ov39owOQVi=X5FFw%2BuQ=qZ9zYi5anA@mail.gmail.com> <20130113224800.GS1410@funkthat.com> <50F33B02.6040303@freebsd.org>
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On Sun, Jan 13, 2013 at 2:53 PM, Nathan Whitehorn <nwhitehorn@freebsd.org> wrote: > On 01/13/13 14:48, John-Mark Gurney wrote: >> Peter Wemm wrote this message on Sun, Jan 13, 2013 at 14:26 -0800: >>> On Sun, Jan 13, 2013 at 12:29 PM, John-Mark Gurney <jmg@funkthat.com> wrote: >>>> Adrian Chadd wrote this message on Sat, Jan 12, 2013 at 23:44 -0800: >>>>> >>>>> People are still ironing out kinks/differences with clang. Anyone >>>>> saying otherwise is likely pushing an agenda. :-) >>>>> >>>>> Thus I think adding clang-only code to the system right now is very, >>>>> very premature. There still seem to be reasons to run systems on GCC >>>>> instead of clang. >>>>> >>>>> If you have a need for new instruction support, perhaps look at adding >>>>> it to our base GCC for the time being? >>>> >>>> I did look at it briefly, but I don't know gcc's internals, and it would >>>> take me 5+ hours to do it, while someone who does know gcc would take >>>> abount a half an hour (just a guess)... I don't have the free time I >>>> used to, otherwise I would of done it by now.. >>> >>> It seems to me that since clang is the default compiler for the >>> platforms that have AES-NI that the following could be done: >>> >>> * get the inline AES-NI stuff in and debugged and solid. >>> * .. without breaking the existing gcc-compatible code >>> * once the support is solid, decide what the appropriate thing to do for gcc is. >>> >>> .. so long as the existing code doesn't get broken. >>> >>> Trying to do backwards compatibility port to gcc with a moving target >>> has potential to be a work multiplier. >> >> I already have a gcc compatible version of an improved AES-NI for >> amd64... The real question is, do I improve things further by using >> intrinsics which means we can share code between amd64 and i386 and get >> great performance from both, or do I simply make a seperate version >> for i386 that is gcc compatible, but not as good performance... >> >> Though a lot of this last little bit of performance questions isn't too >> useful since the overhead of the crypto framework and geom introduces >> a significant overhead already... >> >> I'm not too interesting in creating AES-NI v2 module and having two >> versions that do the same thing just because of a compiler issue... >> >> So I'm going to go with the plan of making an i386 and gcc compatible >> version... it'll still be a 4x+ performance over the existing code... >> This also means we could back port it to 9-stable if we wanted to... >> >> Thanks for the input... >> > > This also raises the interesting question of whether we want to bother > supporting things like AES-NI on i386 at all. It's a legacy/embedded > architecture at this point, in my opinion, and the people who run it > probably don't care about fancy new features like this. A related > question is whether we want to have any clang-only features in the kernel... It wasn't so much an issue of being clang-only, but rather the antique gcc+binutils not having full support on i386. The code would work fine with later versions of gcc/binutils, intel's compiler and clang. Just not with the old gcc + old binutils on i386. -- Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com; KI6FJV bitcoin:188ZjyYLFJiEheQZw4UtU27e2FMLmuRBUE
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