linux-kernel - Re: [PATCH] x86: don't compile vsmp

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Date:	Wed, 25 Mar 2009 16:58:59 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ravikiran G Thirumalai <kiran@...lex86.org>
CC:	Ingo Molnar <mingo@...e.hu>, Yinghai Lu <yinghai@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	shai@...lex86.org
Subject: Re: [PATCH] x86: don't compile vsmp_64 for 32bit

Ravikiran G Thirumalai wrote:
> The point in this thread was, is_vsmp_box() needs to be meaningful even when
> CONFIG_X86_VSMP is not on.  This is needed because is_vsmp_box() is used to
> determine if the platform has reliable tscs.
>   

Well, as I said, that code is inoperative at present.  But aside from 
that, how well will a non-VSMP kernel work on your hardware, with a 
normal cacheline, etc.  Is the tsc stability really all that important, 
given that the kernel should notice if the tsc is busted pretty quickly 
anyway.

unsynchronized_tsc() just returns a guess anyway, and if you don't have 
X86_FEATURE_CONSTANT_TSC set, then it will return unstable for your 
hardware anyway, even without the is_vsmp_box() test.

Failing that, you could add yourself to bad_tsc_dmi_table[] and have 
that mark the tsc as unstable (you have DMI, right?).

    J

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