From: Suzuki K Poulose <suzuki.poulose@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: <linux-arm-kernel@lists.infradead.org>, <mark.rutland@arm.com>,
<ard.biesheuvel@linaro.org>, <marc.zyngier@arm.com>,
<will.deacon@arm.com>, <linux-kernel@vger.kernel.org>,
<kvmarm@lists.cs.columbia.edu>,
"Christoffer Dall" <christoffer.dall@linaro.org>, <nd@arm.com>
Subject: Re: [PATCH v3 2/2] arm64: Support systems without FP/ASIMD
Date: Tue, 15 Nov 2016 10:42:41 +0000 [thread overview]
Message-ID: <3fe7dcce-97ef-54ad-fc3b-8d23bcaa066a@arm.com> (raw)
In-Reply-To: <20161114114858.GB3096@e104818-lin.cambridge.arm.com>
On 14/11/16 11:48, Catalin Marinas wrote:
> Hi Suzuki,
>
>> +static inline bool system_supports_fpsimd(void)
>> +{
>> + return !cpus_have_const_cap(ARM64_HAS_NO_FPSIMD);
>> +}
>
> Any particular reason why using negation instead of a ARM64_HAS_FPSIMD?
> A potential problem would be the default cpus_have_const_cap()
> implementation and the default static key having a slight performance
> impact.
The negation was chosen to avoid hotpatching in the most common case.
But as you said, it has an impact on the other side. I think doing
a one time hotpatching at boot time is more optimal than penalising
a bunch of other users throughout the execution. I will take a look
at changing it back to a ARM64_HAS_FPSIMD.
>> },
>> + {
>> + /* FP/SIMD is not implemented */
>> + .capability = ARM64_HAS_NO_FPSIMD,
>> + .def_scope = SCOPE_SYSTEM,
>> + .min_field_value = 0,
>> + .matches = has_no_fpsimd,
>> + },
>
> If we go for negation, I don't think we need a min_field_value at all,
> the matching is done by the has_no_fpsimd() function.
You're right.
Suzuki
next prev parent reply other threads:[~2016-11-15 12:20 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-08 13:56 [PATCH v3 0/2] " Suzuki K Poulose
2016-11-08 13:56 ` [PATCH v3 1/2] arm64: Add hypervisor safe helper for checking constant capabilities Suzuki K Poulose
2016-11-08 18:11 ` Will Deacon
2016-11-08 13:56 ` [PATCH v3 2/2] arm64: Support systems without FP/ASIMD Suzuki K Poulose
2016-11-14 11:48 ` Catalin Marinas
2016-11-15 10:42 ` Suzuki K Poulose [this message]
2016-11-11 13:41 ` [PATCH v3 0/2] " Marc Zyngier
2016-11-14 11:08 ` Catalin Marinas
2016-11-16 18:11 ` Catalin Marinas
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