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Subject: Re: [PATCH v6 1/3] x86/fpu: track AVX-512 usage of tasks
To:     Andi Kleen <ak@linux.intel.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Aubrey Li <aubrey.li@intel.com>, mingo@redhat.com,
        peterz@infradead.org, hpa@zytor.com, tim.c.chen@linux.intel.com,
        dave.hansen@intel.com, arjan@linux.intel.com,
        linux-kernel@vger.kernel.org
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From:   "Li, Aubrey" <aubrey.li@linux.intel.com>
Message-ID: <6695cf98-17e8-df5f-4dac-264435e2aea5@linux.intel.com>
Date:   Wed, 19 Dec 2018 08:26:30 +0800
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On 2018/12/19 5:38, Andi Kleen wrote:
>> I misunderstood, you mean 32bit kernel, not 32bit machine. Theoretically 32bit
>> kernel can use AVX512, but not sure if anyone use it like this. get_jiffies_64()
>> includes jiffies_lock ops so not good in context switch. So I want to use raw
>> jiffies_64 here. jiffies is a good candidate but it has wraparound overflow issue.
>> Other time source are expensive here.
>>
>> Should I limit the code only running on 64bit kernel? 
> 
> Yes making it 64bit only should be fine.
> 


> Other alternative would be to use 32bit jiffies on 32bit. I assume
> wrapping is not that big a problem here.
> 

Thomas, is this acceptable?

Thanks,
-Aubrey