linux-kernel - RE: [RFC PATCH v2 1/2] x86/fpu: detect AVX task

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Date:   Tue, 13 Nov 2018 10:25:54 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'Li, Aubrey'" <aubrey.li@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Aubrey Li <aubrey.li@...el.com>
CC:     "mingo@...hat.com" <mingo@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "tim.c.chen@...ux.intel.com" <tim.c.chen@...ux.intel.com>,
        "arjan@...ux.intel.com" <arjan@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [RFC PATCH v2 1/2] x86/fpu: detect AVX task

From: Li, Aubrey
> Sent: 12 November 2018 01:41
...
> VZEROUPPER instruction resets the init state. If context switch happens
> to occur exactly after VZEROUPPER instruction, XINUSE bitmap is empty(all
> zeros), which indicates the task is not using AVX. That's why the state
> decay count is used here.

Isn't there an obvious optimisation to execute VZEROALL during system call
entry?
If that is done does any of this actually work?

	David
 

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