linux-kernel - Re: [PATCH v2 1/9] x86/cpu/topology: Add CPU type to struct cpuinfo

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Message-ID: <20240709012418.jyzkxvp3h4p2oda4@desk>
Date: Mon, 8 Jul 2024 18:24:18 -0700
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: Borislav Petkov <bp@...en8.de>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	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>,
	Brice Goglin <brice.goglin@...il.com>,
	Mario Limonciello <mario.limonciello@....com>,
	Perry Yuan <Perry.Yuan@....com>,
	Dapeng Mi <dapeng1.mi@...ux.intel.com>
Subject: Re: [PATCH v2 1/9] x86/cpu/topology: Add CPU type to struct
 cpuinfo_topology

On Thu, Jul 04, 2024 at 01:07:24AM +0200, Borislav Petkov wrote:
> On Fri, Jun 28, 2024 at 10:32:09AM -0700, Pawan Gupta wrote:
> > On Fri, Jun 28, 2024 at 10:03:05AM +0200, Borislav Petkov wrote:
> > > On Thu, Jun 27, 2024 at 01:44:06PM -0700, Pawan Gupta wrote:
> > > > The hw_cpu_type is populated in the below debugfs file:
> > > > 
> > > >   # cat /sys/kernel/debug/x86/topo/cpus/#
> > > 
> > > What "below debugfs file"? A '#'?
> > 
> > That is the number of the CPU. If it is causing confusion, I can will
> > change it to N, or say # means the number of the CPU.
> 
> Or drop that sentence completely.

Ok.

> > > > +static void topo_set_hw_cpu_type(struct cpuinfo_x86 *c)
> > > > +{
> > > > +	c->topo.hw_cpu_type = X86_HW_CPU_TYPE_UNKNOWN;
> > > > +
> > > > +	if (c->x86_vendor == X86_VENDOR_INTEL && c->cpuid_level >= 0x1a)
> > > > +		c->topo.hw_cpu_type = cpuid_eax(0x1a) >> X86_CPU_TYPE_INTEL_SHIFT;
> > > > +}
> > > 
> > > Why isn't this happening in cpu/intel.c? And then you don't need yet
> > > another silly function.
> > 
> > I was preferring to keep the topology related code in one place. Would it
> > make sense to keep it in Intel specific leg in parse_topology() as below:
> 
> I guess.
> 
> Although looking around this code, I wonder why is this hw_cpu_type part of
> the topology and not part of cpuinfo_x86 directly?
> 
> struct cpuinfo_topology has all the IDs but the type? Feels out of place
> there.

The draft version had it in cpuinfo_x86, but it later got moved to
cpuinfo_topology as it appears to be topology related. Below is from AMD
documentation:

  E.4.24 Function 8000_0026—Extended CPU Topology

  CPUID Fn8000_0026 reports extended topology information for logical
  processors, including asymmetric and heterogenous topology descriptions.
  Individual logical processors may report different values in systems with
  asynchronous and heterogeneous topologies.
  https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/programmer-references/24594.pdf

I can move it back to cpuinfo_x86 if you feel strongly about it.