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optimal CPU_FLAGS_X86 settings, and, does it even matter?
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ohum
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PostPosted: Tue Nov 28, 2017 4:42 am    Post subject: optimal CPU_FLAGS_X86 settings, and, does it even matter? Reply with quote

[Moderator note: this was originally a thread necromancy response to Cpu_flags_x86 from 2015, but there was no reason to attach it to that thread. I split it and all then-present responses to this thread. -Hu]

I'm planning to use
Code:
CPU_FLAGS_X86="aes apic avx mmx mmxext pae pclmul popcnt smp sse sse2 sse3 sse4_1 sse4_2 ssse3 xop"

my /proc/cpuinfo is
Code:
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 rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm epb tpr_shadow vnmi flexpriority ept vpid fsgsbase smep erms xsaveopt dtherm ida arat pln pts


Thoughts? Does this even matter?
If I'm correct in understanding, this sets the defaults, which can be overridden.
What is the recommended way to deal with CPU_FLAGS_X86?

Thanks! :)
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fedeliallalinea
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PostPosted: Tue Nov 28, 2017 6:51 am    Post subject: Re: optimal CPU_FLAGS_X86 settings, and, does it even matter Reply with quote

ohum wrote:
What is the recommended way to deal with CPU_FLAGS_X86?

You can use app-portage/cpuid2cpuflags program for set correct CPU_FLAGS_X86
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krinn
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PostPosted: Tue Nov 28, 2017 2:17 pm    Post subject: Reply with quote

Code:
cpuid2cpuflags | sed 's/: /="/;s/$/"/' >> /etc/portage/make.conf

why cpuid2cpuflags doesn't just output it to be use as-is?
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fedeliallalinea
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PostPosted: Tue Nov 28, 2017 2:24 pm    Post subject: Reply with quote

krinn wrote:
Code:
cpuid2cpuflags | sed 's/: /="/;s/$/"/' >> /etc/portage/make.conf

why cpuid2cpuflags doesn't just output it to be use as-is?

What's wrong?
Code:
$ cpuinfo2cpuflags-x86
CPU_FLAGS_X86="aes avx mmx mmxext pclmul popcnt sse sse2 sse3 sse4_1 sse4_2 ssse3"

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krinn
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PostPosted: Tue Nov 28, 2017 4:52 pm    Post subject: Reply with quote

must have an old version :)
Code:
cpuid2cpuflags
CPU_FLAGS_X86: aes avx avx2 f16c fma3 mmx mmxext popcnt sse sse2 sse3 sse4_1 sse4_2 ssse3


ah well
Code:
equery b cpuid2cpuflags
 * Searching for cpuid2cpuflags ...
app-portage/cpuid2cpuflags-4 (/usr/bin/cpuid2cpuflags)

where did you get that cpuinfo2cpuflags-x86 from?
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fedeliallalinea
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PostPosted: Tue Nov 28, 2017 6:19 pm    Post subject: Reply with quote

krinn wrote:
where did you get that cpuinfo2cpuflags-x86 from?

Code:
$ equery b cpuinfo2cpuflags-x86
 * Searching for cpuinfo2cpuflags-x86 ...
app-portage/cpuid2cpuflags-1 (/usr/lib/python-exec/python3.4/cpuinfo2cpuflags-x86)
app-portage/cpuid2cpuflags-1 (/usr/lib/python-exec/python2.7/cpuinfo2cpuflags-x86)
app-portage/cpuid2cpuflags-1 (/usr/bin/cpuinfo2cpuflags-x86 -> ../lib/python-exec/python-exec2)

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krinn
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PostPosted: Wed Nov 29, 2017 1:19 am    Post subject: Reply with quote

It confirm older is better :D
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fedeliallalinea
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PostPosted: Wed Nov 29, 2017 7:03 am    Post subject: Reply with quote

krinn wrote:
It confirm older is better :D

Old is always better :wink: :P
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audiodef
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PostPosted: Tue Feb 06, 2018 4:30 pm    Post subject: Reply with quote

Why did the output format change? I've had to mask version 5, it's less helpful.
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The_Great_Sephiroth
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PostPosted: Tue Feb 06, 2018 5:22 pm    Post subject: Reply with quote

So I am trying to follow this, but what is the difference here. I have always used cpuinfo2cpuflags as we were instructed to do so when the CPU_FLAGS_X86 was added.
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fedeliallalinea
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PostPosted: Tue Feb 06, 2018 5:42 pm    Post subject: Reply with quote

audiodef wrote:
Why did the output format change? I've had to mask version 5, it's less helpful.

Because now hint for activate is
Code:
                        elog 'Please note that the output has changed in v2. The new format is suitable'
                        elog 'both for Portage and Paludis. To use it, e.g.:'
                        elog
                        elog '  $ echo "*/* $(cpuid2cpuflags)" > /etc/portage/package.use/00cpuflags'
                        elog
                        elog '(you may need to convert package.use into a directory if you want to use'
                        elog ' separate file as presented here)'


I don't like this solution and I continue to use CPU_FLAGS_X86 in make.conf, but
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NeddySeagoon
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PostPosted: Tue Feb 06, 2018 6:49 pm    Post subject: Reply with quote

ohum,

CPU_FLAGS_X86 settings, and, does it even matter

The first part of your question has been addressed above.

The second part, does it matter seems to have got lost.
It matters to the few applications that have hand optimised code segments that are selected at build time.
If you want a list of those ebuilds, run
Code:
qgrep -l -i CPU_FLAGS_X86

qgrep belongs to app-portage/portage-utils.

If you use any of those applications, you we get performance improvements with correctly set CPU_FLAGS_X86.

Even that is a little simplistic as not all packages offer all CPU_FLAGS_X86 and not all processors offer all CPU_FLAGS_X86.
Looking at sys-fs/dd-rescue, it offers cpu_flags_x86_avx2 and cpu_flags_x86_sse4_2 so if your CPU does not have them, dd-rescue won't benefit.
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