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Old 05-09-2021, 07:56 PM   #31
Micah
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Optimization flags are overrated. Back in the day, I had a beast of a PC (AMD Athlon yadda yadda) and it Ran Gentoo for years with optimal optimization flags set. One day, something broke and I switch back to Slackware... Everything ran faster on a base install: -Os > -O3 for whatever reason...

I do still have a couple of VIA C7-D (i686 compatible, but it's not... i586 really.) - I do reconfigure the kernel for the C7 enhancements which fixes some ACPI bugs. -- So you can optimize the kernel if needed.

As for multimedia, I don't do much there but mplayer/mencoder detect CPU optimizations at runtime to improve performance. I doubt EVERYTHING does that, but you should check.
 
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Old 05-10-2021, 05:00 AM   #32
tauon
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Originally Posted by usr345 View Post
Now I see that there will be almost no improvement. But can I compile some graphics app for my native sandy bridge CPU and look how it works? There may be improvement. I don't know: VLC, xine. But in this case I'll probably need to recompile the kernel too.

I am switching to x64 Slackware when 15.0 comes out.
For multimedia apps you can benefit from using AVX instructions (SIMD instructions with eight 32-bit single-precision floating point registers according to Wikipedia), but I'm not sure how it works with 32bits (I've never try to do that, but here (https://community.intel.com/t5/Intel...rs/td-p/771334) people say the number of AVX registers is reduced). Linux Kernel can't benefit from that because it doesn't use floating-point math (at least I read that as a requirement for kernel developers).

As for Slackware, VLC is available via slackbuilds.org, not via standard "official" Slackware repos. Thus, you need to configure and compile it for yourself in any case, so you can try to find a set of compiler flags working for your platform better then in the provided SlackBuild).
 
Old 05-11-2021, 01:30 AM   #33
usr345
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Originally Posted by tauon View Post
Linux Kernel can't benefit from that because it doesn't use floating-point math (at least I read that as a requirement for kernel developers).
From SIMD it can't. But remember, there are SYSENTER/SYSEXIT instructions, starting from Pentium II. It allows a faster switch from user mode to kernel mode.

If we compile both the kernel and userspace code with them, their interaction will become faster.
 
Old 05-11-2021, 07:29 AM   #34
chemfire
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Originally Posted by usr345 View Post
From SIMD it can't. But remember, there are SYSENTER/SYSEXIT instructions, starting from Pentium II. It allows a faster switch from user mode to kernel mode.

If we compile both the kernel and userspace code with them, their interaction will become faster.
Again though you are talking about a small performance jump at the cost of abandoning at lot of hardware. While it might not be entirely insignificant its not game changing either. Anyone with a performance critical application has moved on to x86-64 or has solved their problem a long time ago at this point. If x86 was still the mainline platform this would be an argument. x86 systems are legacy at this point. The focus on the x86 port, should be supporting as wide a range of those systems as is practical not squeezing the last drop of performance out some of the last generation parts.

If you need performance and want to use enhanced features use x86-64
 
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Old 05-12-2021, 02:34 AM   #35
tauon
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Originally Posted by usr345 View Post
From SIMD it can't. But remember, there are SYSENTER/SYSEXIT instructions, starting from Pentium II. It allows a faster switch from user mode to kernel mode.
There is a nice blog post on that: http://www.os2museum.com/wp/sysenter-where-are-you/, so you don't have SYSENTER support for every i686. I don't know if the generic i686 linux system uses this instruction.
 
  


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