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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 7 Sep 2021 18:43:46 -0700
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Subject: Re: ipv4/tcp.c:4234:1: error: the frame size of 1152 bytes is larger
 than 1024 bytes [-Werror=frame-larger-than=]
To:     Nathan Chancellor <nathan@kernel.org>
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        Mathias Nyman <mathias.nyman@intel.com>,
        Johannes Berg <johannes@sipsolutions.net>,
        Jakub Kicinski <kuba@kernel.org>,
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        Ariel Elior <aelior@marvell.com>,
        GR-everest-linux-l2@marvell.com, Wei Liu <wei.liu@kernel.org>,
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        open list <linux-kernel@vger.kernel.org>,
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On Tue, Sep 7, 2021 at 6:35 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> I think a lot of them have just copied the x86 code (it was 4k long
> ago), without actually understanding all the details.

Just to put the x86 number in perspective: it was raised to 8192 back
in 2013, with the comment

    x86/cpu: Increase max CPU count to 8192

    The MAXSMP option is intended to enable silly large numbers of
    CPUs for testing purposes.  The current value of 4096 isn't very
    silly any longer as there are actual SGI machines that approach
    6096 CPUs when taking HT into account.

    Increase the value to a nice round 8192 to account for this and
    allow for short term future increases.

so on the x86 side, people have actually done these things.

Other architectures? I think some IBM power9 machines can hit 192
cores (with SMT4 - so NR_CPUS of 768), but I don't think there's been
an equivalent of an SGI for anything but x86.

But admittedly I haven't checked or followed those things. I could
easily imagine some boutique super-beefy setup.

               Linus