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

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Message-ID: <20240703230724.GEZoXZrIavchI2Kj-P@fat_crate.local>
Date: Thu, 4 Jul 2024 01:07:24 +0200
From: Borislav Petkov <bp@...en8.de>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
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 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.

For some reason lately it seems to me folks feel the need to explain what the
patch does. Even if that is visible from the diff.

> I thought about that, but the other fields are also printed without a
> preceding "0x":
> 
>           seq_printf(m, "initial_apicid:      %x\n", c->topo.initial_apicid);
>           seq_printf(m, "apicid:              %x\n", c->topo.apicid);
> 	  ...
> 
> I will change those too, probably in a separate patch.

Yes please.

> > > +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.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette