linux-kernel - Re: Linux patch disabling AVX when eagerfpu is turned off

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Message-ID: <56A13B88.1090505@zytor.com>
Date:	Thu, 21 Jan 2016 12:11:52 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Dave Hansen <dave.hansen@...el.com>,
	Leonid Shatz <leonid.shatz@...ellosystems.com>,
	"'Ingo Molnar'" <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	"'Yu-cheng Yu'" <yu-cheng.yu@...el.com>,
	"'Andy Lutomirski'" <luto@...capital.net>,
	"'Borislav Petkov'" <bp@...en8.de>,
	"'Fenghua Yu'" <fenghua.yu@...el.com>,
	"'Linus Torvalds'" <torvalds@...ux-foundation.org>,
	"'Oleg Nesterov'" <oleg@...hat.com>,
	"'Peter Zijlstra'" <peterz@...radead.org>,
	"'Quentin Casasnovas'" <quentin.casasnovas@...cle.com>,
	"'Ravi V. Shankar'" <ravi.v.shankar@...el.com>,
	"'Sai Praneeth Prakhya'" <sai.praneeth.prakhya@...el.com>,
	"'Thomas Gleixner'" <tglx@...utronix.de>
Cc:	liran.alon@...ellosystems.com, mendel.aizner@...ellosystems.com,
	"'Elazar Leibovich'" <elazar.leibovich@...ellosystems.com>,
	"'Eyal Moscovici'" <eyal.moscovici@...ellosystems.com>,
	gil.hoffer@...ellosystems.com
Subject: Re: Linux patch disabling AVX when eagerfpu is turned off - possibly
 not required

On 01/21/16 12:08, Dave Hansen wrote:
> On 01/21/2016 02:33 AM, Leonid Shatz wrote:
>> In view of above findings we would like to suggest to double check if
>> disabling AVX together with "eagerfpu off" is actually required and is a
>> real necessity. It would be helpful to consult with Intel engineers
>> regarding related design details.
> 
> Hi Leonid,
> 
> Thanks for the report!
> 
> Are you aware of any actual eagerfpu=off use in practice, or is this
> mostly a theoretical concern?
> 

Looking into this, FWIW.

	-hpa