linux-kernel - Re: [RFC PATCH] x86: Kill notsc

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Message-ID: <20151019081610.GB20028@pd.tnic>
Date:	Mon, 19 Oct 2015 10:16:10 +0200
From:	Borislav Petkov <bp@...e.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	x86-ml <x86@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] x86: Kill notsc

On Sun, Oct 18, 2015 at 09:47:21PM -0700, Andy Lutomirski wrote:
> I'm a bit confused.  Is it currently the case that, if you boot a
> normal kernel on a TSC-less machine without notsc, it fails?

No, it shouldn't fail because we're checking CPUID flags.

The point of this patch is purely cleaning up stuff and getting rid
of all the notsc/tsc_disabled logic. What is more tempting, however,
is getting rid of the static key in native_sched_clock. It is almost
pointless complexity and we don't really need it.

AFAIK, only some early 486s and 586s don't have TSC and they can disable
CONFIG_X86_TSC. Which they do, actually, if you choose M486 or M586 in
Kconfig.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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