linux-kernel - Re: [PATCH v6 1/3] x86/fpu: track AVX-512 usage of tasks

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Message-ID: <20181218213826.GI25620@tassilo.jf.intel.com>
Date:   Tue, 18 Dec 2018 13:38:26 -0800
From:   Andi Kleen <ak@...ux.intel.com>
To:     "Li, Aubrey" <aubrey.li@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Aubrey Li <aubrey.li@...el.com>, mingo@...hat.com,
        peterz@...radead.org, hpa@...or.com, tim.c.chen@...ux.intel.com,
        dave.hansen@...el.com, arjan@...ux.intel.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 1/3] x86/fpu: track AVX-512 usage of tasks

> 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.

-Andi