linux-kernel - Re: [patch 5/9] x86: Cure per CPU madness on UP

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Date: Mon, 18 Mar 2024 18:27:55 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Linus Torvalds <torvalds@...uxfoundation.org>
Cc: Guenter Roeck <linux@...ck-us.net>, LKML <linux-kernel@...r.kernel.org>,
 x86@...nel.org, Uros Bizjak <ubizjak@...il.com>,
 linux-sparse@...r.kernel.org, lkp@...el.com,
 oe-kbuild-all@...ts.linux.dev, Arnd Bergmann <arnd@...nel.org>
Subject: Re: [patch 5/9] x86: Cure per CPU madness on UP

On Sat, Mar 16 2024 at 02:11, Thomas Gleixner wrote:
> On Fri, Mar 15 2024 at 16:23, Linus Torvalds wrote:
> The amount of subtle SMP=n fallout has been kinda exponentially
> increasing over the years and it's just putting burden on the wrong
> people. TBH, I'm tired of this nonsense.

And for the fun of it I hacked Kconfig to allow a SMP=y NR_CPUS=1 build
and checked the size of vmlinux:

                64-bit          32-bit
SMP, NCPUS=1    38438400        22110177
UP              38393703        21682041
Delta              44697          428076
                     0.1%              2%              

The UP savings are not really impressive...

Let me look what it actually takes to do that.

Thanks,

        tglx