48 lines
1.6 KiB
Text
48 lines
1.6 KiB
Text
Title: CPU_FLAGS_X86 introduction
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Author: Michał Górny <mgorny@gentoo.org>
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Content-Type: text/plain
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Posted: 2015-01-28
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Revision: 2
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News-Item-Format: 1.0
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Display-If-Keyword: amd64
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Display-If-Keyword: ~amd64
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Display-If-Keyword: x86
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Display-If-Keyword: ~x86
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The USE flags corresponding to the instruction sets and other features
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specific to the x86 (amd64) architecture are being moved into a separate
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USE flag group called CPU_FLAGS_X86.
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In order not to lose CPU-specific optimizations, users will be required
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to update their make.conf (and package.use) file. For example, if
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the following USE flags were present:
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USE="mmx mmxext sse sse2 sse3"
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Those flags need to be copied into:
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CPU_FLAGS_X86="mmx mmxext sse sse2 sse3"
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Please note that the same CPU_FLAGS_X86 variable is used both on x86
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and amd64 systems.
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When in doubt, you can consult the flag descriptions using one of
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the commonly available tools, e.g. `equery uses` from gentoolkit:
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$ equery uses media-video/ffmpeg
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Most of the flag names match /proc/cpuinfo names, with the notable
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exception of SSE3 which is called 'pni' in /proc/cpuinfo (please also
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do not confuse it with distinct SSSE3).
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To help users enable the correct USE flags, we are providing a Python
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script that generates the correct value using /proc/cpuinfo. It can be
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found in the app-portage/cpuinfo2cpuflags package:
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$ emerge -1v app-portage/cpuinfo2cpuflags
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$ cpuinfo2cpuflags-x86
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In order to ensure safe migration and maintain compatibility with
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external repositories, it is recommended to preserve the old USE
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settings for a period of one year or until no package of interest is
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still using them.
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