linux-kernel - Re: [PATCH 4/5] x86/kernel: Provide a means to disable TSC ART

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Message-ID: <20171004092704.mm4q5ivrlfrcj6sk@hirez.programming.kicks-ass.net>
Date:   Wed, 4 Oct 2017 11:27:04 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     mike.travis@....com
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Bin Gao <bin.gao@...ux.intel.com>,
        Prarit Bhargava <prarit@...hat.com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Andrew Banman <andrew.banman@....com>,
        Russ Anderson <russ.anderson@....com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 4/5] x86/kernel: Provide a means to disable TSC ART

On Mon, Oct 02, 2017 at 10:12:18AM -0500, mike.travis@....com wrote:
>  static void detect_art(void)
>  {
>  	unsigned int unused[2];
>  
> -	if (boot_cpu_data.cpuid_level < ART_CPUID_LEAF)
> +	if (boot_cpu_data.cpuid_level < ART_CPUID_LEAF || tsc_art_disabled)
>  		return;
>  
>  	/* Don't enable ART in a VM, non-stop TSC and TSC_ADJUST required */


So why can't we use is_uv_system() here an for the tsc_adjust thing?

Also (and I hate the name) tsc_multi_sync_resets is the reason you
cannot use ART, I don't think it makes sense to introduce yet another
knob.