From: Catalin Marinas <catalin.marinas@arm.com>
To: Ionela Voinescu <ionela.voinescu@arm.com>
Cc: will@kernel.org, maz@kernel.org, corbet@lwn.net,
linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH 1/4] arm64: add support for the AMU extension v1
Date: Thu, 10 Oct 2019 18:20:58 +0100 [thread overview]
Message-ID: <20191010172058.GD40923@arrakis.emea.arm.com> (raw)
In-Reply-To: <20190917134228.5369-2-ionela.voinescu@arm.com>
Hi Ionela,
On Tue, Sep 17, 2019 at 02:42:25PM +0100, Ionela Voinescu wrote:
> +#ifdef CONFIG_ARM64_AMU_EXTN
> +
> +/*
> + * This per cpu variable only signals that the CPU implementation supports the
> + * AMU but does not provide information regarding all the events that it
> + * supports.
> + * When this amu_feat per CPU variable is true, the user of this feature can
> + * only rely on the presence of the 4 fixed counters. But this does not
> + * guarantee that the counters are enabled or access to these counters is
> + * provided by code executed at higher exception levels.
> + */
> +DEFINE_PER_CPU(bool, amu_feat) = false;
> +
> +static void cpu_amu_enable(struct arm64_cpu_capabilities const *cap)
> +{
> + if (has_cpuid_feature(cap, SCOPE_LOCAL_CPU)) {
> + pr_info("detected CPU%d: Activity Monitors extension\n",
> + smp_processor_id());
> + this_cpu_write(amu_feat, true);
> + }
> +}
Sorry if I missed anything as I just skimmed through this series. I
can't see the amu_feat used anywhere in these patches, so on its own it
doesn't make much sense.
I also can't see the advantage of allowing mismatched CPU
implementations for this feature. What's the intended use-case?
Thanks.
--
Catalin
next prev parent reply other threads:[~2019-10-10 17:21 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-17 13:42 [PATCH 0/4] arm64: ARMv8.4 Activity Monitors support Ionela Voinescu
2019-09-17 13:42 ` [PATCH 1/4] arm64: add support for the AMU extension v1 Ionela Voinescu
2019-10-10 17:20 ` Catalin Marinas [this message]
2019-10-11 10:31 ` Ionela Voinescu
2019-10-11 14:31 ` Catalin Marinas
2019-09-17 13:42 ` [PATCH 2/4] arm64: trap to EL1 accesses to AMU counters from EL0 Ionela Voinescu
2019-09-17 13:42 ` [PATCH 3/4] arm64/kvm: disable access to AMU registers from kvm guests Ionela Voinescu
2019-09-17 13:42 ` [PATCH 4/4] Documentation: arm64: document support for the AMU extension Ionela Voinescu
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