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

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Date:   Wed, 4 Oct 2017 07:15:17 -0700
From:   Mike Travis <mike.travis@....com>
To:     Peter Zijlstra <peterz@...radead.org>
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 10/4/2017 2:27 AM, Peter Zijlstra wrote:
> 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?

I could.  I just thought that there may be future system arches that
need the same facility?
> 
> 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.
> 
Okay.  I wasn't sure if there might be different causes for wanting one
condition over the other.  So does this mean change this later test to
use is_uv_system() or tsc_multi_sync_resets?

Thanks.