linux-kernel - Re: [PATCH v7 04/12] platform/x86: hfi: Introduce AMD Hardware Feedback Interface Driver

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Message-ID: <20241202113512.GA8562@noisy.programming.kicks-ass.net>
Date: Mon, 2 Dec 2024 12:35:12 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Mario Limonciello <mario.limonciello@....com>
Cc: Borislav Petkov <bp@...en8.de>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
	"H . Peter Anvin" <hpa@...or.com>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	"Gautham R . Shenoy" <gautham.shenoy@....com>,
	Perry Yuan <perry.yuan@....com>,
	Brijesh Singh <brijesh.singh@....com>,
	Li RongQing <lirongqing@...du.com>,
	"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <linux-kernel@...r.kernel.org>,
	"open list:ACPI" <linux-acpi@...r.kernel.org>,
	"open list:AMD PSTATE DRIVER" <linux-pm@...r.kernel.org>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
	Shyam Sundar S K <Shyam-sundar.S-k@....com>
Subject: Re: [PATCH v7 04/12] platform/x86: hfi: Introduce AMD Hardware
 Feedback Interface Driver

On Sat, Nov 30, 2024 at 08:06:55AM -0600, Mario Limonciello wrote:

> +/**
> + * struct amd_hfi_cpuinfo - HFI workload class info per CPU
> + * @cpu:		cpu index
> + * @cpus:		mask of cpus associated with amd_hfi_cpuinfo
> + * @class_index:	workload class ID index
> + * @nr_class:		max number of workload class supported
> + * @amd_hfi_classes:	current cpu workload class ranking data
> + *
> + * Parameters of a logical processor linked with hardware feedback class
> + */
> +struct amd_hfi_cpuinfo {
> +	int		cpu;
> +	cpumask_var_t	cpus;

This appears unused.

> +	s16		class_index;
> +	u8		nr_class;
> +	struct amd_hfi_classes	*amd_hfi_classes;
> +};
> +
> +static DEFINE_PER_CPU(struct amd_hfi_cpuinfo, amd_hfi_cpuinfo) = {.class_index = -1};
> +
> +static int amd_hfi_alloc_class_data(struct platform_device *pdev)
> +{
> +	struct amd_hfi_cpuinfo *hfi_cpuinfo;
> +	struct device *dev = &pdev->dev;
> +	int idx;
> +	int nr_class_id;
> +
> +	nr_class_id = cpuid_eax(AMD_HETERO_CPUID_27);
> +	if (nr_class_id < 0 || nr_class_id > 255) {
> +		dev_err(dev, "failed to get number of supported classes: %d\n",
> +			nr_class_id);
> +		return -EINVAL;
> +	}
> +
> +	for_each_present_cpu(idx) {

This uses present, but does not have means of handling changes to
present. Does this want to be possible?