linux-kernel - Re: [RFC PATCH 0/15] x86: Remove support for TSC-less and CX8-less CPUs

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Message-ID: <c329a9ed268eef90306be6529ac13d46322c6709.camel@physik.fu-berlin.de>
Date: Tue, 06 May 2025 15:54:06 +0200
From: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To: "Maciej W. Rozycki" <macro@...am.me.uk>, "H. Peter Anvin" <hpa@...or.com>
Cc: Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org, "Ahmed S .
 Darwish" <darwi@...utronix.de>, Andrew Cooper <andrew.cooper3@...rix.com>,
 Ard Biesheuvel	 <ardb@...nel.org>, Arnd Bergmann <arnd@...nel.org>,
 Borislav Petkov <bp@...en8.de>,  Dave Hansen <dave.hansen@...ux.intel.com>,
 John Ogness <john.ogness@...utronix.de>, Linus Torvalds	
 <torvalds@...ux-foundation.org>, Peter Zijlstra <peterz@...radead.org>, 
 Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH 0/15] x86: Remove support for TSC-less and CX8-less
 CPUs

On Tue, 2025-05-06 at 14:48 +0100, Maciej W. Rozycki wrote:
>  In fact running old hardware is one aspect of portability verification, 
> for example I run PCIe stuff off my Pentium MMX and Alpha hardware, and 
> conversely I run conventional PCI stuff off my POWER9 (no port I/O!) and 
> RISC-V hardware.  That has triggered numerous bugs, fixed over the years.

I agree with that stance. Building and running Debian on various architectures
has enabled use to find obscure bugs that did not trigger easily on x86_64
or arm64.

I remember one nasty bug in the DMA code that initially showed on ia64 only
and it was only when someone finally ran into the same problem on x86_64 that
it was actually fixed.

> 
> (fddi0 is the fast intranet interface, eth0 is the slow external one).  
> It's a luggable integrated computer BTW, a Dolch PAC 60, very nice and 
> compact, previously used by a field engineer for network fault isolation.
> 
>  I've already mentioned the maintenance of the defxx driver (it is also an 
> exercise in portability, with defxx supporting 3 host bus attachments).
> 
>  This is also my backup box for GNU toolchain (GCC/glibc/GDB) verification 
> for the i386 target.  It has actually proved recently to still have some 
> commercial relevance (again, for portability verification), but who says 
> the use of Linux is supposed to be solely commercial even nowadays?

I fully agree with this. Cross-architecture testing really helps finding hidden
bugs and it's also fun ;-).

>  The origin of Linux is obvious and I wouldn't be around at all let alone 
> for so many years if not for my enthusiasm solely for the technical merit 
> of Linux (following my earlier passion for processors and systems) 
> accompanied by the fairness of the GNU GPL, with any commercial aspect 
> being at most distantly relevant and a late comer into the game.
> 
>  So yes, count me in as a passionate systems software engineer with a 
> fondness for running odd configurations for the sake of experimentation 
> (and consequently a portability exercise) and please do not deprive me of 
> my enthusiasm.

Count me in as well.

PS: No, we don't have to bring back ia64 for that matter ;-).

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer
`. `'   Physicist
  `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913