linux-kernel - Re: [RFC PATCH -v2.1] x86: Kill notsc

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Date:	Mon, 16 Nov 2015 21:02:15 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>
Cc:	Peter Zijlstra <peterz@...radead.org>, x86-ml <x86@...nel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH -v2.1] x86: Kill notsc

On 11/16/15 13:25, Thomas Gleixner wrote:
> On Mon, 16 Nov 2015, Borislav Petkov wrote:
>> -/*
>> - * disable flag for tsc. Takes effect by clearing the TSC cpu flag
>> - * in cpu/common.c
>> - */
>> -int __init notsc_setup(char *str)
>> +/* Disable the TSC feature flag to avoid further TSC use. */
>> +int __init notsc_setup(void)
>>  {
>> +#ifndef CONFIG_X86_TSC
>>  	setup_clear_cpu_cap(X86_FEATURE_TSC);
> 
> This is silly, really.
> 
> If CONFIG_X86_TSC is disabled then we should just not compile tsc.c at
> all and map cpu_has_tsc and stuff depending on it to false.
> 

CONFIG_X86_TSC means TSC is obligatory, not that it is supported.

	-hpa


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