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gcc 4.9 neue konfiguration
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Joined: 14 Feb 2004
Posts: 944
Location: Germany

PostPosted: Wed Jan 06, 2016 7:40 pm    Post subject: gcc 4.9 neue konfiguration Reply with quote

Hallo Leute,

laut /proc/cpuinfo habe ich folgenden Proczessor:
Intel(R) Core(TM) i5-5200U CPU @ 2.20GHz
Dies sollte eine Broadwell Intel Cpu sein.

Laut /proc/cpuinfo hat dieser Processor folgende Flags:
fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 fma cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch ida arat epb pln pts dtherm intel_pt tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid rdseed adx smap xsaveopt

Im Handbuch vom GCC 4.9.3 passend zum gcc steht folgendes:


Intel Broadwell CPU with 64-bit extensions, MOVBE, MMX, SSE,
RDSEED, ADCX and PREFETCHW instruction set support

Die Flags: PREFETCHW taucht z.B. nicht unter cpuinfo auf. Daher bin ich verunsichert.
Kann ich folgendes in meiner make.conf vermerken:
CFLAGS="-broadwell -O2 -pipe"

Bisher fahre ich diese Einstellung:
CFLAGS="-march=core-avx2 -O2 -pipe"

Diese taucht aber nicht mehr in der GCC Beschreibung auf.

Gruss Jörg
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Klaus Meier

Joined: 18 Apr 2005
Posts: 2908
Location: Bozen

PostPosted: Thu Jan 07, 2016 6:26 am    Post subject: Reply with quote

Das kann der gcc ganz alleine feststellen. Das machst du genau so:
CFLAGS="-march=native -O2 -pipe"

Des weiteren gibt es ja noch die CPU_FLAGS. Dazu kopiere ich dir mal die entsprechende News. Du hast sie aber selber auf dem Rechner, du bekommst ja die entsprechende Meldung, die du mit "eselect news read" lesen solltest.
  Title                     CPU_FLAGS_X86 introduction
  Author                    Michał Górny <>
  Posted                    2015-01-28
  Revision                  2

The USE flags corresponding to the instruction sets and other features
specific to the x86 (amd64) architecture are being moved into a separate
USE flag group called CPU_FLAGS_X86.

In order not to lose CPU-specific optimizations, users will be required
to update their make.conf (and package.use) file. For example, if
the following USE flags were present:

  USE="mmx mmxext sse sse2 sse3"

Those flags need to be copied into:

  CPU_FLAGS_X86="mmx mmxext sse sse2 sse3"

Please note that the same CPU_FLAGS_X86 variable is used both on x86
and amd64 systems.

When in doubt, you can consult the flag descriptions using one of
the commonly available tools, e.g. `equery uses` from gentoolkit:

  $ equery uses media-video/ffmpeg

Most of the flag names match /proc/cpuinfo names, with the notable
exception of SSE3 which is called 'pni' in /proc/cpuinfo (please also
do not confuse it with distinct SSSE3).

To help users enable the correct USE flags, we are providing a Python
script that generates the correct value using /proc/cpuinfo. It can be
found in the app-portage/cpuinfo2cpuflags package:

  $ emerge -1v app-portage/cpuinfo2cpuflags
  $ cpuinfo2cpuflags-x86

In order to ensure safe migration and maintain compatibility with
external repositories, it is recommended to preserve the old USE
settings for a period of one year or until no package of interest is
still using them.

cpuinfo2cpuflags sagt dir, was du setzen musst.
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