linux-kernel - Re: [PATCH 0/15] x86/xsaves: Optimize xstate context switch by xsaves/xrstors

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Date:	Mon, 26 May 2014 12:37:25 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Fenghua Yu <fenghua.yu@...el.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Asit K Mallick <asit.k.mallick@...el.com>
CC:	linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH 0/15] x86/xsaves: Optimize xstate context switch by xsaves/xrstors

On 05/26/2014 10:01 AM, Fenghua Yu wrote:
> From: Fenghua Yu <fenghua.yu@...el.com>
> 
> With ever growing extended state registers (xstate) on x86 processors, kernel
> needs to cope with issue of growing memory space occupied by xstate. The xsave
> area is holding more and more xstate registers, growing from legacy FP and
> SSE to AVX, AVX2, AVX-512, MPX, and Intel PT.
> 
> The recently introduced compacted format of xsave area saves xstates only
> for enabled states. This patch set saves the xsave area space per process
> in compacted format by xsaves/xrstors instructions.

Are we going to want to encourage userspace to do something like
sticking vzeroupper right before each syscall to make any
xsaves/xrestores faster?

--Andy

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