Exporting cpu instruction set to kernel .config file

Guddla Rupesh rupeshforu3 at gmail.com
Thu Mar 3 10:21:09 EST 2022

Pentium MMX was launched about 30 years ago and at that time video
processing was new and there was no proper hardware just to play any video
file I mean if you play any video file video playback stops sometimes and
resume after some time.

At present there is lot of development in video hardware and at the same
time new technologies in both hardware and software has been evolved.
Coming into hardware CPUs with integrated graphics came and coming into
software many video and audio codecs have been developed like h265, vpx,
av1, aac, opus etc.,.Of these aac and opus are audio codecs which produces
lowest disk size at reasonable quality and h265, av1 are video codecs which
provides lowest disk size at reasonable quality.

Most of the time I download videos from youtube and other sources which are
of large size. When you record a video in android smartphone it takes
around 600 mb for 3 minutes 50 seconds and it uses h265 codec. It is
difficult to store such files in my android smartphone.

Mostly I use Linux and ffmpeg tool to compress these video files. Of h265
and av1 aom encoders. av1 aom encoder provide lowest disk size at lowest
video bitrate. H265 encoding and decoding are supported in all hardware
including pc and smartphone but unfortunately av1 files are not supported
in none but definitely I think that it will become defacto standard in

If h265 encoding takes 1 minute then aom av1 encoding takes about 10
minutes. If video acceleration is present the encoding takes about 7
minutes. Video acceleration come into action only if GPU is detected
properly and the necessary drivers are installed. If the system can detect
opecl version of GPU then av1 encoding takes about 5 minutes through ffmpeg.

As MMX was trending about 30 years ago I think that latest processors have
vector instructions for video transcoding or encoding like avx2 or avx 512,
simd etc.,. These new instructions are not present in 15 years back

As 64 bit processor came into action around 20 years back nowadays
processors are 10 times are greater in performance than old.

I think that all the kernels shipped by distros are not considering latest
processors instruction set. I think that even windows is doing the same.

If opencl is detected properly any application can have improvement in
performance about 10 percent.

I can't find any option to set opencl in the Linux kernel config file or in
any of the kernel source files.

Atleast I am lucky to select option core 2 in the main .config file of

Finally my request is there any way to export instruct set of my cpu to the
kernel configuration and so after compilation my video encoding takes less
time than previous.

If it's a difficult task leave it and if it's possible try to suggest how
to do so.

On Thu, 3 Mar 2022, 6:56 am FMDF, <fmdefrancesco at gmail.com> wrote:

> On Thu, 3 Mar 2022, 02:05 FMDF, <fmdefrancesco at gmail.com> wrote:
>> On Wed, 2 Mar 2022, 17:57 Guddla Rupesh, <rupeshforu3 at gmail.com> wrote:
>>> I have seen the config from /proc/config.gz and found that processor
>>> family as generic x86 64.
>>> Actually my system consists of i3 10th gen comet lake 10100 which has
>>> integrated graphics and pci express 4.0 and also lots of new instructions
>>> like avx2, sse4 etc.,.
>> Therefore, in .config, you should enable x86-64. That's it. Simple.
>>> The main reason of compiling source code of kernel is it detects all my
>>> hardware and provide support for opencl, video acceleration etc.,. But I
>>> can't find any option to select my processor especially comet lake or
>>> atleast skylake and instead there is an option called core2 in the section
>>> processor family.
>> There are no Cometlake or Skylake options for kernel compilation. Your
>> recent CPU is already supported and the whole ISA is available. Compilers
>> know your system and they know which instructions are better suited for
>> your applications and kernel code.
>>> Finally I have disabled secure boot mode in bios and compiled source
>>> code successfully and now I am able to boot into the latest build kernel
>>> but there is no difference in performance between old and new kernels.
>> Why have you disabled secure boot mode? If performance concerns you,
>> don't worry about it: there is no loss of performance with secure boot.
>>> I think that normal kernel shipped by the distro is generic and it
>>> doesn't have support for latest instructions like avx2, sse4 etc.,. To get
>>> support we must compile kernel with lots of tuning.
>> No, you're wrong :)
>> Just select the highest available processor family (I can't recall now if
>> it is "core2" or "generic x86_64", it's the last of the list in the
>> "processor family" section if you use "make menuconfig") and the entire
>> instruction set of Intel x86-64 will be enabled and available.
>> There is neither a "CONFIG_GENERATION_11" nor similar options.
>>> I have exported the modules running on system and disable others by
>>> running the command
>>> make localmodconfig
>> Beware that using "localmodconfig" disables the build of lots of modules
>> you may need in the future. It relies on the current system configuration.
>> When you'll add new devices you'll have to enable their drivers and
>> recompile the modules.
>>> What I want is " is there any way to export my cpu instruction set to
>>> kernel .config file and compile kernel and install the modules.".
>>> If I can compile kernel source code then my Linux system will run at
>>> extreme speeds never before.
>> You might tune the optimization flags of (e.g., GCC's "-On", for n=0,1,2,
>> and  others) but I strongly advise you to not do this because (1) it is
>> clear that you don't understand how the code is compiled and (2) you
>> probably won't get the results you think you should get.
>> Regards,
>> Fabio M. De Francesco
> I was about to forget three more things:
> 1) Read Torin's answer because he is right.
> 2) Don't touch configuration's options that you don't know. For instance,
> do you know if you should enable "CONFIG_CORE_SCHED"? Just think that you
> can inadvertently disable Intel Hyperthreading with that option.
> 3) Just copy your distro's .config and re-compile :)
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