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Re: Ability to further support 32bit architectures

On 1/12/24 13:07, Alan Corey wrote:
Are you forgetting that 64 bit is slower?  In the arm world where it's easily switchable 64 bit is pokey when you don't need it.
Thank Alan, to put numbers behind that, linuxcnc has a thing called latency-test on an rpi4b the armhf kernel I built from 4.19 srcs, can respond to an irq in 12 microseconds, this in 2018. in 2023, an arm64 rt-preempt kernel can only do that in around 50 microseconds. The huge majority of that time is a increased size of the stack frame it has to put away and then reload the environment to handle the interrupt.
On Fri, Jan 12, 2024, 12:54 PM <rhys@neoquasar.org <mailto:rhys@neoquasar.org>> wrote: 



    Sent from my mobile device.

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    *Sent:* Friday, January 12, 2024 10:11
    *To:* rhys@neoquasar.org <mailto:rhys@neoquasar.org>
    *Cc:* noloader@gmail.com <mailto:noloader@gmail.com>;
    debian-kernel@lists.debian.org
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    *Subject:* Re: Ability to further support 32bit architectures

    <rhys@neoquasar.org <mailto:rhys@neoquasar.org>> 于2024年1月12日周五
    23:59写道：
     >
     > Keeping in mind that I am new to this arena...
     >
     > I have some Intel systems - both 64-bit and 32-bit - that I might
    be able to use as build platforms.
     >

    I guess all of your hardwares are 64bit. You setup different OS on them.

    No. I have multiple 32-bit systems, one of which is Intel.

     > What does the Debian team need from me to be able to use these
    systems?
     >

    It's not about performance of hardware. It is about some limitation
    of 32bit.
    2 examples for it:
        1. if we use 32bit value for time, it will overflow in 2038, then
    your time will be shown as 1900.
    https://en.wikipedia.org/wiki/Year_2038_problem
    <https://en.wikipedia.org/wiki/Year_2038_problem>
        2. A single process (or maybe APP, not precisely), can only use UP
    to 4GiB RAM.
            In fact on most system the value is less than 4GiB:
               on intel32, it is 3GiB
               on mips32, it is 2GiB
            But currently, it is not enough, for example, when we build a
    big APP, it will need much more RAM.
            The RAM does install in your Rack, but you can NOT use it.
    https://en.wikipedia.org/wiki/3_GB_barrier
    <https://en.wikipedia.org/wiki/3_GB_barrier>

     > I can't guarantee they'll be FAST, but I'll do what I can to make
    them EFFECTIVE.
     >

    If you are really need 32bit system. Maybe you can say out why you
    *REALLY* need it.
    For most users, the suggestion is: upgrade to 64bit.


    That's not at all what I was asking or talking about.

    --J



Cheers, Gene Heskett.
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