linux-kernel - Re: [PATCH 2/5] x86/kernel: Skip TSC test and error messages if already unstable

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Date:   Thu, 12 Oct 2017 08:17:34 -0700
From:   Mike Travis <mike.travis@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     Peter Zijlstra <peterz@...radead.org>,
        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 2/5] x86/kernel: Skip TSC test and error messages if
 already unstable



On 10/12/2017 4:17 AM, Thomas Gleixner wrote:
> On Thu, 5 Oct 2017, mike.travis@....com wrote:
> 
>> If the TSC has already been determined to be unstable, then checking
>> TSC ADJUST values is a waste of time and generates unnecessary error
>> messages.
>>
>> Signed-off-by: Mike Travis <mike.travis@....com>
>> Reviewed-by: Dimitri Sivanich <dimitri.sivanich@....com>
>> Reviewed-by: Russ Anderson <russ.anderson@....com>
>> Reviewed-by: Peter Zijlstra <peterz@...radead.org>
>> ---
>>   arch/x86/kernel/tsc_sync.c |    8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> --- linux.orig/arch/x86/kernel/tsc_sync.c
>> +++ linux/arch/x86/kernel/tsc_sync.c
>> @@ -38,6 +38,10 @@ void tsc_verify_tsc_adjust(bool resume)
>>   	if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
>>   		return;
>>   
>> +	/* Skip unnecessary error messages if TSC already unstable */
>> +	if (check_tsc_unstable())
>> +		return;
>> +
>>   	/* Rate limit the MSR check */
>>   	if (!resume && time_before(jiffies, adj->nextcheck))
>>   		return;
>> @@ -89,6 +93,10 @@ bool tsc_store_and_check_tsc_adjust(bool
>>   	if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
>>   		return false;
>>   
>> +	/* Skip unnecessary error messages if TSC already unstable */
>> +	if (check_tsc_unstable())
>> +		return false;
>> +
>>   	rdmsrl(MSR_IA32_TSC_ADJUST, bootval);
>>   	cur->bootval = bootval;
>>   	cur->adjusted = bootval;
> 
> This hunk rejects and I really can't figure out against which tree that
> would apply.

My current merge tree happens to be 4.13.0-rc1 which was the latest when 
I started this patch submission.  I can update my merge tree and reapply 
if need be?

> 
> Btw, there are two incarnations of tsc_store_and_check_tsc_adjust().
> Shouldn't the !SMP variant get the same treatment?

I could add it though I'm not sure the point?  If it's only one CPU 
would TSC's being out of sync become a question?
> 
> Thanks,
> 
> 	tglx
>