linux-kernel - Re: [PATCH 07/21] X86_64, UV: Disable Obsolete APIC ID fixup code used only on UV1

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Date:	Tue, 3 May 2016 09:35:12 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Mike Travis <travis@....com>
Cc:	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Len Brown <len.brown@...el.com>,
	Dimitri Sivanich <sivanich@....com>,
	Russ Anderson <rja@....com>,
	John Estabrook <estabrook@....com>,
	Andrew Banman <abanman@....com>,
	Nathan Zimmer <nzimmer@....com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/21] X86_64, UV: Disable Obsolete APIC ID fixup code
 used only on UV1


* Mike Travis <travis@....com> wrote:

> +config X86_UV1_SUPPORTED
> +	bool "SGI Ultraviolet Series 1 Supported"
> +	depends on X86_UV

So I still think it's much simpler if we simply eliminate this Kconfig 
complication and have it all compatible. AFAICS the runtime impact on newer 
systems comes down mostly to a single unlikely branch:

>  static unsigned int x2apic_get_apic_id(unsigned long x)
>  {
> -	unsigned int id;
> +	if (likely(!uv1_apic_driver))
> +		return x;

Thanks,

	Ingo