From: Catalin Marinas <catalin.marinas@arm.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: "Jia He" <justin.he@arm.com>, "Will Deacon" <will@kernel.org>,
"Mark Rutland" <mark.rutland@arm.com>,
"James Morse" <james.morse@arm.com>,
"Marc Zyngier" <maz@kernel.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
"Suzuki Poulose" <Suzuki.Poulose@arm.com>,
"Punit Agrawal" <punitagrawal@gmail.com>,
"Anshuman Khandual" <anshuman.khandual@arm.com>,
"Jun Yao" <yaojun8558363@gmail.com>,
"Alex Van Brunt" <avanbrunt@nvidia.com>,
"Robin Murphy" <robin.murphy@arm.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Ralph Campbell" <rcampbell@nvidia.com>,
hejianet@gmail.com, "Kaly Xin" <Kaly.Xin@arm.com>
Subject: Re: [PATCH v4 1/3] arm64: cpufeature: introduce helper cpu_has_hw_af()
Date: Wed, 18 Sep 2019 17:49:25 +0100 [thread overview]
Message-ID: <20190918164925.GB41588@arrakis.emea.arm.com> (raw)
In-Reply-To: <20190918142017.GC9880@bombadil.infradead.org>
On Wed, Sep 18, 2019 at 07:20:17AM -0700, Matthew Wilcox wrote:
> On Wed, Sep 18, 2019 at 09:19:12PM +0800, Jia He wrote:
> > +/* Decouple AF from AFDBM. */
> > +bool cpu_has_hw_af(void)
> > +{
> > + return (read_cpuid(ID_AA64MMFR1_EL1) & 0xf);
> > +}
> > +
>
> Do you really want to call read_cpuid() every time? I would have thought
> you'd want to use the static branch mechanism to do the right thing at
> boot time. See Documentation/static-keys.txt.
We do have a static branch mechanism for other CPU features but mostly
because on some big.LITTLE systems, the CPUs may differ slightly so we
only advertise the common features.
I guess here the additional instructions for reading and checking the
CPUID here would be lost in the noise compared to the actual page
copying.
--
Catalin
next prev parent reply other threads:[~2019-09-18 16:49 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-18 13:19 [PATCH v4 0/3] fix double page fault on arm64 Jia He
2019-09-18 13:19 ` [PATCH v4 1/3] arm64: cpufeature: introduce helper cpu_has_hw_af() Jia He
2019-09-18 14:20 ` Matthew Wilcox
2019-09-18 16:49 ` Catalin Marinas [this message]
2019-09-18 14:20 ` Suzuki K Poulose
2019-09-18 16:45 ` Catalin Marinas
2019-09-19 1:55 ` Justin He (Arm Technology China)
2019-09-18 13:19 ` [PATCH v4 2/3] arm64: mm: implement arch_faults_on_old_pte() on arm64 Jia He
2019-09-18 13:19 ` [PATCH v4 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared Jia He
2019-09-18 14:00 ` Kirill A. Shutemov
2019-09-18 18:00 ` Catalin Marinas
2019-09-19 15:00 ` Kirill A. Shutemov
2019-09-19 15:41 ` Catalin Marinas
2019-09-19 15:51 ` Kirill A. Shutemov
2019-09-19 2:16 ` Jia He
2019-09-19 14:57 ` Kirill A. Shutemov
2019-09-19 15:02 ` Justin He (Arm Technology China)
2019-09-18 19:35 ` kbuild test robot
2019-09-19 1:46 ` Justin He (Arm Technology China)
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