linux-kernel - Re: [PATCH RESEND] x86/cpu/topology: remove limit of CPUs due to noapic on x86

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Message-ID: <Z0Q3ZNoQsoiCAiiA@gmail.com>
Date: Mon, 25 Nov 2024 09:37:56 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Fernando Fernandez Mancera <ffmancera@...eup.net>
Cc: linux-kernel@...r.kernel.org, tglx@...utronix.de, x86@...nel.org
Subject: Re: [PATCH RESEND] x86/cpu/topology: remove limit of CPUs due to
 noapic on x86_64


* Fernando Fernandez Mancera <ffmancera@...eup.net> wrote:

> On x86_64 the command line parameter "noapic" should not limit the
> number of possible CPUs, as it only limits the use of IRQ sharing or
> device IRQ remapping. Only on x86_32 the command line parameter
> "nolapic" limits the number of possible CPUs to one. This restores the
> behavior previous to the rework of possible CPU management.

So what's the motivation? Arguably the x86-64 boot option behavior was 
weird: a working local APIC is very much needed to have an SMP system.

If we want to disable IRQ sharing or device IRQ remapping, then that 
should have an appropriately named boot command line option. Does some 
system require that perhaps?

Thanks,

	Ingo