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Shall portage support Function Multi-Versioning?
yes
15%
 15%  [ 3 ]
no
40%
 40%  [ 8 ]
don't care
45%
 45%  [ 9 ]
Total Votes : 20

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skunk
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PostPosted: Fri Apr 06, 2018 3:35 pm    Post subject: Support for Function Multi-Versioning (FMV) Reply with quote

[Moderator note: changed title from support for fmv to Support for Function Multi-Versioning (FMV) because FMV in computing commonly means "Full Motion Video", which is completely unrelated to the topic of this thread; changed poll question from shall portage support fmv? to Shall portage support Function Multi-Versioning? for the same reason. -Hu]

hey!
since i use my desktop (ivybridge) to build packages for my laptop (skylake) i would really like to see function multi-versioning support in portage...
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pjp
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PostPosted: Fri Apr 06, 2018 4:43 pm    Post subject: Reply with quote

Quote:
optimized for Intel
So, no.

Although I voted "don't care" as long as the extraneous code isn't clogging up my system.
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Ant P.
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PostPosted: Fri Apr 06, 2018 6:36 pm    Post subject: Reply with quote

Someone should remind Intel that GCC exists.

You're not going to get much benefit by building fat binaries for two *lake chips in any case. If you're that hard pressed for speed, better to use hardware without Meltdown.
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skunk
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PostPosted: Fri Apr 06, 2018 6:50 pm    Post subject: Reply with quote

pjp wrote:
Quote:
optimized for Intel
So, no.

Although I voted "don't care" as long as the extraneous code isn't clogging up my system.

i wonder if you've cared to read the whole article or just the title... :roll:
the concept is about building application that runs on old generation cpu's and may leverage on more modern cpu extensions as well.
in my case i would be able to build an application that may use avx2 extensions and run on both my desktop (without avx2) and my laptop (with avx2).
and yes, even amd or arm processors would benefit from such a technique, it's not just another intel thing...
i know the most benefit are for binary distributions, however it would be just another nice (imho) choice even for gentoo... :)
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skunk
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PostPosted: Fri Apr 06, 2018 6:56 pm    Post subject: Reply with quote

Ant P. wrote:
Someone should remind Intel that GCC exists.

You're not going to get much benefit by building fat binaries for two *lake chips in any case. If you're that hard pressed for speed, better to use hardware without Meltdown.

uh? those are gcc-6 and glibc-2-26 new features... 8O
i'll be happy to buy a power9 desktop when they'll start to sell them at a reasonable price and a risc-v laptop when there will be one available...
no intel/amd/arm fanboy here, just someone who buys hardware that suits my needs... :wink:
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NeddySeagoon
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PostPosted: Fri Apr 06, 2018 7:52 pm    Post subject: Reply with quote

skunk,

I'm a don't care leaning towards no. This feature cannot be implemented without a performance penalty.
I can't spare the RAM and in some cases the HDD space for the bloat.
Being a Gentoo user everything is tailored to the individual target anyway.

I can see binary distros and purveyors of binaries liking it but in my opinion, its rather like systemd.
Use it if you want to, just don't force it on me.
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pjp
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PostPosted: Fri Apr 06, 2018 9:19 pm    Post subject: Reply with quote

skunk wrote:
i wonder if you've cared to read the whole article or just the title... :roll:
I didn't presume that the title would be false or inaccurate, and as I don't use Intel CPUs, the rest seemed not relevant. So, yeah. :roll:
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Tony0945
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PostPosted: Fri Apr 06, 2018 10:22 pm    Post subject: Reply with quote

Don't see any need. Run the appropriate march/mtune in your make.conf. This is for binary packages not source packages. If you're building for distribution to Ubuntu or Arch, yeah! There may be a small set of Gentoo users building binaries for Windows or cross-comopling. So, no, no special effort. Developer effort should go into fixing bugs or speeding up portage.

EDIT: spelling


Last edited by Tony0945 on Mon Apr 09, 2018 1:02 am; edited 1 time in total
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geki
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PostPosted: Sat Apr 07, 2018 7:29 am    Post subject: Reply with quote

My POV as software developer:
Luckily, most (if not all) software, that cares for performance and is in need thereof, does this or similar already. AFAI watch compiles flying by (i.e.: ffmpeg, mesa and others). :o

So, nothing really to be done; from this POV.
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bunder
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PostPosted: Sat Apr 07, 2018 9:31 am    Post subject: Reply with quote

I would rather upgrade the ivybridge to something newer than skylake and use distcc. 8)
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The_Document
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PostPosted: Sun Apr 08, 2018 10:17 pm    Post subject: Reply with quote

No cause its likely to break things. Developers should do it right and implement modern instruction sets right into their code.
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krinn
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PostPosted: Mon Apr 09, 2018 4:41 am    Post subject: Reply with quote

wonderful option for binaries distro
totally useless for gentoo, space & memory eater for no benefits.
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Goverp
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PostPosted: Mon Apr 09, 2018 7:25 am    Post subject: Reply with quote

a) Gentoo is about choice
b) Gentoo is a meta-distribution
Ergo, people should be able to build FMV distributions using Gentoo.
But I voted "Don't care"
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mv
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PostPosted: Mon Apr 09, 2018 9:34 am    Post subject: Reply with quote

geki wrote:
My POV as software developer:

That's exactly what the whole story is about.
Quote:
Luckily, most (if not all) software, that cares for performance and is in need thereof, does this or similar already.

This is plainly false: Only software that cares for performance and has bundled all libraries (at least the ones which could gain from the optimization) can do this.
For libraries which are not bundled but which are pulled in as dependencies, this is exactly what portage would need to care about.
Typical example: numpy (which would profit from an optimized cblas/lapack)
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mv
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PostPosted: Mon Apr 09, 2018 9:51 am    Post subject: Reply with quote

NeddySeagoon wrote:
This feature cannot be implemented without a performance penalty.

A performance penalty only at startup (depending on the glibc implementation perhaps even only once at startup of the machine).
Quote:
I can't spare the RAM and in some cases the HDD space for the bloat.

RAM cost is only a few bytes in glibc. HDD cost is none except if you target multiple architectures. In the latter case, it is only the code for the additional architectures itself which take HDD space.
Quote:
I can see binary distros and purveyors of binaries

Gentoo users are such purveyors if they build binary packages for several machines (which not necessarily all have the same processor features). I think it is a rather frequent setting to have one "build" machine and to distribute the binaries to other systems. Currently, you have to choose the lowest common denominator on these systems.
Quote:
Use it if you want to, just don't force it on me.

Nothing would be forced: From the user side an implementation would probably be rather similar to how ABI_X86=.... currently behaves, i.e. you select "your" architecture. If you do not select a second/third/forth/... architecture nothing changes for you (also no disk space overhead), except that perhaps a different directory path is used for the generated library (lib/arch/ instead of lib/)

Edit: Typos and reformulations to make things clearer.
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skunk
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PostPosted: Mon Apr 09, 2018 10:27 am    Post subject: Reply with quote

mv wrote:
Quote:
I can see binary distros and purveyors of binaries

Gentoo users are such purveyors if they build binary packages for several machines (which not necessarily all have the same processor features). I think it is a rather frequent setting to have one "build" machine and to distribute the binaries to other systems. Currently, you have to choose the lowest common denominator on these systems.

that's exactly what i mean as use case, moreover in my specifically case:
  • i need to build packages for a modern mobile weak but power efficient processor and i want to use an older but powerful processor for that for obvious reasons
  • my job consist in deploying private clouds for my customers using linux containers and want to be able to move those containers around between an heterogeneous set of hosts without having to rebuild the container images on the destination host
of course, as mv pointed out, i'm sure it could be absolutely opt in without jamming it into anybody's throat... :wink:
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NeddySeagoon
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PostPosted: Mon Apr 09, 2018 2:04 pm    Post subject: Reply with quote

skunk,

I use (cross) distcc in these situations.
My main amd64 /no-multilib/ system builds for arm, arm64, x86 and another low power amd64 system.

I understand the problem but adding bloat is not a part of the solution on a source based distro,

Going back to lowest common denominator builds, all systems wait at the same speed, so its only a few performance critical apps where in actually makes a difference.
e.g. libreoffice spends most of its time waiting for keystrokes.
Video processing can use all the speed it can get, but you don't do that on out of date hardware if you can avoid it.
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mv
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PostPosted: Mon Apr 09, 2018 3:03 pm    Post subject: Reply with quote

@skunk: Do you plan to implement it, e.g. in a google SOC project?

Otherwise, I am afraid that this whole poll is rather useless. A poll alone will not inspire an implementation. An implementation is rather tedious; much harder than ABI_X86= since in a sense it is a strict superset of this.
When I think how many years ABI_X86 took... not only the pure implementation itself, but also the fights how it should be implemented and many competing half-finished implementation attempts...
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skunk
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PostPosted: Wed Apr 11, 2018 2:30 pm    Post subject: Reply with quote

ok guys, i was just asking some opinions about something i've believed could have been useful...
i'll keep doing the lowest common denominator strategy with my servers farm and on my desktop/laptop.

thank you
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