From: "H. Peter Anvin" <hpa@zytor.com>
To: Ingo Molnar <mingo@kernel.org>, Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@suse.de>,
Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>,
"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
Leonid Shatz <leonid.shatz@ravellosystems.com>,
Fenghua Yu <fenghua.yu@intel.com>,
Andy Lutomirski <luto@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH] x86/fpu: Revert earlier patch of Disable AVX when eagerfpu is off
Date: Wed, 9 Mar 2016 10:51:45 -0800 [thread overview]
Message-ID: <56E070C1.6090302@zytor.com> (raw)
In-Reply-To: <20160309124626.GA28660@gmail.com>
On 03/09/2016 04:46 AM, Ingo Molnar wrote:
>
> * Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
>
>> AVX was mistakenly believed to be dependent on eagerfpu switch.
>> This turns out to be false. The earlier patch should be reverted.
>>
>> Original patch:
>> http://git.kernel.org/tip/394db20ca240741a08d472173db13d6f6a6e5a28
>
> So the original patch had a whole host of explanations of why that change is
> correct. This revert should explain where that argumentation was wrong.
>
> Also note that eagerfpu=off is on the way out, on v4.6 we'll switch all CPUs to
> eagerfpu:
>
> 58122bf1d856 x86/fpu: Default eagerfpu=on on all CPUs
>
> and in the not so distant future, if everything goes fine with the eager mode, I'd
> like to drop the lazy FPU context switching code altogether - which will simplify
> a lot of code. At that point the 'eagerfpu' boot option will go away as well.
>
Last I heard the only use case which was seeing trouble with eagerfpu
was KVM during service of I/O events. Might be worth checking into...
-hpa
prev parent reply other threads:[~2016-03-09 18:52 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-23 1:10 [PATCH] x86/fpu: Revert earlier patch of Disable AVX when eagerfpu is off Yu-cheng Yu
2016-03-09 12:46 ` Ingo Molnar
2016-03-09 17:19 ` Yu-cheng Yu
2016-03-09 18:42 ` Ingo Molnar
2016-03-09 18:51 ` H. Peter Anvin [this message]
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