linux-kernel - Re: [PATCH] Calling check_system_tsc_reliable before unsynchronized

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Date:   Tue, 13 Jun 2017 10:47:28 +0800
From:   Zhenzhong Duan <zhenzhong.duan@...cle.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     mingo@...hat.com, hpa@...or.com, x86@...nel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Calling check_system_tsc_reliable before
 unsynchronized_tsc

在 2017/6/13 0:03, Thomas Gleixner 写道:
> On Thu, 8 Jun 2017, Zhenzhong Duan wrote:
>
>> unsynchronized_tsc() checks value of tsc_clocksource_reliable which is set by
>> check_system_tsc_reliable(). It's better to move check_system_tsc_reliable()
>> at
>> front, or else this check makes no sense.
>>
>> Though X86_FEATURE_CONSTANT_TSC is usually set for TSC reliable system, just
>> in
>> case.
>>
>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@...cle.com>
>> ---
>>   arch/x86/kernel/tsc.c |    4 ++--
>>   1 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
>> index 714dfba..a316bdd 100644
>> --- a/arch/x86/kernel/tsc.c
>> +++ b/arch/x86/kernel/tsc.c
>> @@ -1412,11 +1412,11 @@ void __init tsc_init(void)
>>    	use_tsc_delay();
>>   +	check_system_tsc_reliable();
>> +
>>   	if (unsynchronized_tsc())
>>   		mark_tsc_unstable("TSCs unsynchronized");
>>   -	check_system_tsc_reliable();
>> -
> What kind of patch is that? Definitely nothing which can be applied.
To avoid using unassigned variable tsc_clocksource_reliable.
Or what's the purpose of if (tsc_clocksource_reliable) check in 
unsynchronized_tsc()?

-- 
thanks
zduan