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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Wed, 8 Sep 2021 19:00:11 +0200
Message-ID: <CAK8P3a3xjZovRz-iOPOC8jQPNsPcupQ5b3hpx-XNxP=oDqhtkQ@mail.gmail.com>
Subject: Re: ipv4/tcp.c:4234:1: error: the frame size of 1152 bytes is larger
 than 1024 bytes [-Werror=frame-larger-than=]
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Nathan Chancellor <nathan@kernel.org>,
        Naresh Kamboju <naresh.kamboju@linaro.org>,
        Mathias Nyman <mathias.nyman@intel.com>,
        Johannes Berg <johannes@sipsolutions.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Shuah Khan <skhan@linuxfoundation.org>,
        Brendan Higgins <brendanhiggins@google.com>,
        Ariel Elior <aelior@marvell.com>,
        GR-everest-linux-l2@marvell.com, Wei Liu <wei.liu@kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        open list <linux-kernel@vger.kernel.org>,
        Netdev <netdev@vger.kernel.org>, lkft-triage@lists.linaro.org,
        Arnd Bergmann <arnd@arndb.de>,
        "David S. Miller" <davem@davemloft.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Alexei Starovoitov <ast@kernel.org>,
        Eric Dumazet <edumazet@google.com>
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On Wed, Sep 8, 2021 at 3:43 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> 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.

POWER10 was just announced with threads 1920 using SMT8,
I think the latest s390 and sparc64 (from 2017) are in the same
ballpark when using SMT. The largest arm64 I know of was ThunderX3
with 768 threads on dual-socket machines. This got cancelled before
it was shipped to customers, but it's likely that others will exceed that
in the future.

       Arnd