linux-kernel - Re: [PATCH PATCH 1/9] x86/cpu/topology: Add x86_cpu_type to struct cpuinfo

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Date: Tue, 18 Jun 2024 15:03:29 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Mario Limonciello <mario.limonciello@....com>,
 Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org
Cc: daniel.sneddon@...ux.intel.com, tony.luck@...el.com,
 linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
 linux-perf-users@...r.kernel.org, Josh Poimboeuf <jpoimboe@...nel.org>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
 "Rafael J. Wysocki" <rafael@...nel.org>,
 Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
 "Liang, Kan" <kan.liang@...ux.intel.com>,
 Andrew Cooper <andrew.cooper3@...rix.com>, Perry Yuan <Perry.Yuan@....com>
Subject: Re: [PATCH PATCH 1/9] x86/cpu/topology: Add x86_cpu_type to struct
 cpuinfo_topology

On 6/18/24 14:33, Mario Limonciello wrote:
>> +enum x86_topo_cpu_type {
>> +    X86_CPU_TYPE_UNKNOWN        = 0,
>> +    X86_CPU_TYPE_INTEL_ATOM        = 0x20,
>> +    X86_CPU_TYPE_INTEL_CORE        = 0x40,
>> +};
>> +
...
> What do you think about having a common enum rather with words that are
> marketing strings? 

They're not really marketing strings.  They really are architectural and
have specific functional meaning just like ->x86_model and ->x86_family.

For instance, we are effectively doing this today:

	if (c->cpu_x86_vfm == INTEL_ALDER_LAKE &&
	    c->cpu_type == X86_CPU_TYPE_INTEL_ATOM)
		setup_force_cpu_bug(FOO);

That check is truly specific to the core being an "ATOM" and not being
an efficient core.  There might be a future non-Atom efficient CPU or a
future non-Core performance CPU.

We very well might have a use in the future to tag a processor as
"efficient" or "performance" in a vendor-neutral manner.  That mechanism
could very well be derived from ->cpu_type.  But I think that's actually
independent from Pawan's series.