Re: [gentoo-dev] Review: desc/cpu_flags_x86.desc

[Michał Górny]

Dnia 2015-01-19, o godz. 11:38:26
Alexis Ballier <aballier@g.o> napisał(a):

> On Sun, 18 Jan 2015 21:44:05 +0100
> Michał Górny <mgorny@g.o> wrote:
>
> > Hello,
> >
> > I would like to commit the following flags as cpu_flags_x86_desc.
> > The list combines global USE flags with some local USE flags I've been
> > able to find.
> >
> >
> > 3dnow - Use the 3DNow! instruction set
> > 3dnowext - Use the Enhanced 3DNow! instruction set
> > aes-ni - Enable support for Intel's AES instruction set (aes in
> > cpuinfo) avx - Adds support for Advanced Vector Extensions
> > instructions avx2 - Adds support for Advanced Vector Extensions 2
> > instructions fma - Use the Fused Multiply Add instruction set
> > mmx - Use the MMX instruction set
> > mmxext - Use the Extended MMX instruction set (intersection of
> > Enhanced 3DNow! and SSE instruction sets) (3dnowext or sse in
> > cpuinfo) padlock - Use VIA padlock instructions popcnt - Enable
> > popcnt instruction support sse - Use the SSE instruction set
> > sse2 - Use the SSE2 instruction set
> > sse3 - Use the SSE3 instruction set (pni in cpuinfo)
> > sse4 - Enable SSE4 instruction support
> > sse4_1 - Enable SSE4.1 instruction support
> > sse4_2 - Enable SSE4.2 instruction support
> > sse4a - Enable SSE4a instruction support
> > ssse3 - Use the SSSE3 instruction set
> >
>
> ewwww... are you aware that these descriptions are close to useless ?
> 'foo - enable foo' -> thanks for the information I couldn't have
> guessed...

It's not my fault we have to put some description there!

> you already have more useful ones available:
>
> <flag name="fma3">Enables FMA3 optimizations: AMD processors starting
>   with Piledriver architecture and Intel Haswell based processors or
>   later.</flag>
> <flag name="fma4">Enables FMA4 optimizations: AMD processors starting
> with Bulldozer architecture.</flag>
> <flag name="sse4_2">Enables SSE4.2 optimizations: Nehalem-based Intel
> Core i7 or later.</flag>
> <flag name="ssse3">Faster floating point optimization for SSSE3 capable
> chips (Intel Core 2 and later chips)</flag>
>
> and so on...

Feel free to update them yourself. As far as I'm concerned, those
descriptions are worse than useless because they end up being
confusing. Many CPU lines had weird models with more or less
instruction sets, so brand name aren't really helpful. It's better to
focus on /proc/cpuinfo.

-- 
Best regards,
Michał Górny