linux-kernel - Re: [PATCH 2/2] x86: fix platform info detection in frequency invariance

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Message-ID: <7dffbd70-d7db-6d58-abbb-19006cd9e4a2@intel.com>
Date:   Fri, 20 May 2022 09:44:25 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Giovanni Gherdovich <ggherdovich@...e.cz>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86: fix platform info detection in frequency
 invariance

On 5/20/22 09:10, Giovanni Gherdovich wrote:
>  	if (slv_set_max_freq_ratio(&base_freq, &turbo_freq))
>  		goto out;
>  
> -	if (x86_match_cpu(has_glm_turbo_ratio_limits) &&
> -	    skx_set_max_freq_ratio(&base_freq, &turbo_freq, 1))
> +	if (x86_match_cpu(has_glm_turbo_ratio_limits)) {
> +		skx_set_max_freq_ratio(&base_freq, &turbo_freq, 1);
>  		goto out;
> +	}
>  
> -	if (x86_match_cpu(has_knl_turbo_ratio_limits) &&
> -	    knl_set_max_freq_ratio(&base_freq, &turbo_freq, 1))
> +	if (x86_match_cpu(has_knl_turbo_ratio_limits)) {
> +		knl_set_max_freq_ratio(&base_freq, &turbo_freq, 1);
>  		goto out;
> +	}
>  
> -	if (x86_match_cpu(has_skx_turbo_ratio_limits) &&
> -	    skx_set_max_freq_ratio(&base_freq, &turbo_freq, 4))
> +	if (x86_match_cpu(has_skx_turbo_ratio_limits)) {
> +		skx_set_max_freq_ratio(&base_freq, &turbo_freq, 4);
>  		goto out;
> +	}
>  
>  	if (core_set_max_freq_ratio(&base_freq, &turbo_freq))
>  		goto out;

But didn't the last patch in the series carefully change the return
value for knl_set_max_freq_ratio()?  Now, the only call site is ignoring
the return value?  That seems odd.

Also, this is a mess.  These constructs:

static const struct x86_cpu_id has_knl_turbo_ratio_limits[] = {
        X86_MATCH(XEON_PHI_KNL),
        X86_MATCH(XEON_PHI_KNM),
        {}
};

static const struct x86_cpu_id has_skx_turbo_ratio_limits[] = {
        X86_MATCH(SKYLAKE_X),
        {}
};

static const struct x86_cpu_id has_glm_turbo_ratio_limits[] = {
        X86_MATCH(ATOM_GOLDMONT),
        X86_MATCH(ATOM_GOLDMONT_D),
        X86_MATCH(ATOM_GOLDMONT_PLUS),
        {}
};

are rather goofy.  A single array like rapl_ids[] that points to the
handler function would do us a lot more good here, say:

static const struct x86_cpu_id has_knl_turbo_ratio_limits[] = {
        X86_MATCH(XEON_PHI_KNL, 	&knl_set_max_freq_ratio),
        X86_MATCH(XEON_PHI_KNM, 	&knl_set_max_freq_ratio),
        X86_MATCH(SKYLAKE_X,		&skx_set_max_freq_ratio),
        X86_MATCH(ATOM_GOLDMONT, 	&skx_set_max_freq_ratio),
        X86_MATCH(ATOM_GOLDMONT_D,	&skx_set_max_freq_ratio),
        X86_MATCH(ATOM_GOLDMONT_PLUS,	&skx_set_max_freq_ratio),
	X86_MATCH(ANY,			&core_set_max_freq_ratio),
        {}
};

That would get rid of all the goofy gotos and actually puts all the
logic in one place.  BTW, I'm not 100% sure about the 'ANY' line.  I
think that's how those work, but please double-check me on it.

While it's generally best to keep bug fixes to a minimum, I think this
one is worth a bit of a cleanup because it will remove a bunch of spaghetti.