linux-kernel - Re: [PATCHv2] x86, CPU: Restore MSR_IA32_ENERGY_PERF

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Date:	Fri, 17 Jul 2015 22:39:25 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Laura Abbott <labbott@...oraproject.org>
cc:	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCHv2] x86, CPU: Restore MSR_IA32_ENERGY_PERF_BIAS after
 resume

On Fri, 17 Jul 2015, Laura Abbott wrote:
> v2: Tweaked a few names to be more descriptive

Descriptive by some definition of descriptive. See below.

> +static void init_intel_energy_perf(struct cpuinfo_x86 *c)
> +{
> +	/*
> +	 * Initialize MSR_IA32_ENERGY_PERF_BIAS if BIOS did not.
> +	 * x86_energy_perf_policy(8) is available to change it at run-time
> +	 */
> +	if (cpu_has(c, X86_FEATURE_EPB)) {

Make this 

	if (!cpu_has(c, X86_FEATURE_EPB))
	   	return;

and spare the extra indentation level.

> +		u64 epb;
> +		rdmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb);
> +		if ((epb & 0xF) == ENERGY_PERF_BIAS_PERFORMANCE) {

Ditto

> +			pr_warn_once("ENERGY_PERF_BIAS: Set to 'normal', was 'performance'\n");
> +			pr_warn_once("ENERGY_PERF_BIAS: View and update with x86_energy_perf_policy(8)\n");
> +			epb = (epb & ~0xF) | ENERGY_PERF_BIAS_NORMAL;
> +			wrmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb);
> +		}
> +	}
> +}
>  #ifdef CONFIG_X86_32
> @@ -747,6 +752,7 @@ static const struct cpu_dev intel_cpu_dev = {
>  	.c_detect_tlb	= intel_detect_tlb,
>  	.c_early_init   = early_init_intel,
>  	.c_init		= init_intel,
> +	.c_bsp_resume	= init_intel_energy_perf,

Looking at the resulting code I have no idea WHY
init_intel_energy_perf is set here. So much for descriptive.

This really wants to be bsp_resume() or something like this (add the
pointless intel prefix if it makes your managers happy). That _IS_
actually descriptive.

static void bsp_resume(struct cpuinfo_x86 *c)
{
	/*
	 * Some reasonable comment WHY we call this here.
	 */
	 init_intel_energy_perf(c);
}

Aside of documenting what that resume thing is for and why
init_intel_energy_perf() needs to be called, I'm quite sure that this
will fill up pretty fast with other stuff which gets lost across S/R.

Thanks,

	tglx
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