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([2601:646:c200:7429:f021:f41a:9790:a132]) by smtp.gmail.com with ESMTPSA id b18-v6sm11149765pgk.15.2018.09.26.09.24.39 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 26 Sep 2018 09:24:39 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (1.0) Subject: Re: [RFC PATCH 10/10] x86/fpu: defer FPU state load until return to userspace From: Andy Lutomirski X-Mailer: iPhone Mail (16A366) In-Reply-To: <20180926153229.n5rwlfhuqu42ds6v@linutronix.de> Date: Wed, 26 Sep 2018 09:24:38 -0700 Cc: Bryan O'Donoghue , Denys Vlasenko , Ong@linutronix.de, Boon Leong , linux-kernel@vger.kernel.org, x86@kernel.org, Andy Lutomirski , Paolo Bonzini , =?utf-8?Q?Radim_Kr=C4=8Dm=C3=A1=C5=99?= , kvm@vger.kernel.org, "Jason A. Donenfeld" , Rik van Riel Content-Transfer-Encoding: quoted-printable Message-Id: <176B4B39-6471-401C-A1E1-4B6B3FF157C3@amacapital.net> References: <20180912133353.20595-1-bigeasy@linutronix.de> <20180912133353.20595-11-bigeasy@linutronix.de> <650FC457-7E4C-473A-9E5F-EAFC74F6444B@amacapital.net> <20180919170515.ptqmmpsxrdjsi64j@linutronix.de> <20180926111222.hihueuagmb4qfmtz@linutronix.de> <59E2EBC5-C483-4788-B490-4A3770DBB993@amacapital.net> <20180926153229.n5rwlfhuqu42ds6v@linutronix.de> To: Sebastian Andrzej Siewior Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Sep 26, 2018, at 8:32 AM, Sebastian Andrzej Siewior wrote: >=20 > On 2018-09-26 07:34:09 [-0700], Andy Lutomirski wrote: >>> So I *think* nobody relies on FPU-emulation anymore. I would suggest to >>> get this patch set into shape and then getting rid of >>> CONFIG_MATH_EMULATION? >=20 > Bryan, Denys, does anyone of you rely on CONFIG_MATH_EMULATION? > The manual for Quark claims that the CPU has no FPU and yet the current > kernel (or the yocto v3.14) does not select this option. > Denys added support for some opcodes in 2015 but I didn't figure out > *why* or which CPU in particular requires this. Certainly the early Quark CPUs were, um, crappy. They had so many terrifying= errata that I=E2=80=99m surprised anyone is willing to use them. I would *hope* that all supported Quark CPUs support FPU instructions even i= f they=E2=80=99re microcoded and run extremely slowly.