linux-kernel - Re: [PATCH V2 20/25] perf/x86/intel: Add Alder Lake Hybrid support

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Date:   Thu, 11 Mar 2021 17:32:50 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...ux.intel.com
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org, acme@...nel.org,
        tglx@...utronix.de, bp@...en8.de, namhyung@...nel.org,
        jolsa@...hat.com, ak@...ux.intel.com, yao.jin@...ux.intel.com,
        alexander.shishkin@...ux.intel.com, adrian.hunter@...el.com,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH V2 20/25] perf/x86/intel: Add Alder Lake Hybrid support

On Thu, Mar 11, 2021 at 05:09:25PM +0100, Peter Zijlstra wrote:
> On Wed, Mar 10, 2021 at 08:37:56AM -0800, kan.liang@...ux.intel.com wrote:
> > From: Kan Liang <kan.liang@...ux.intel.com>
> > 
> > Alder Lake Hybrid system has two different types of core, Golden Cove
> > core and Gracemont core. The Golden Cove core is registered to
> > "cpu_core" PMU. The Gracemont core is registered to "cpu_atom" PMU.
> > 
> > The difference between the two PMUs include:
> > - Number of GP and fixed counters
> > - Events
> > - The "cpu_core" PMU supports Topdown metrics.
> >   The "cpu_atom" PMU supports PEBS-via-PT.
> > 
> > The "cpu_core" PMU is similar to the Sapphire Rapids PMU, but without
> > PMEM.
> > The "cpu_atom" PMU is similar to Tremont, but with different
> > event_constraints, extra_regs and number of counters.
> > 
> 
> > +		/* Initialize big core specific PerfMon capabilities.*/
> > +		pmu = &x86_pmu.hybrid_pmu[X86_HYBRID_PMU_CORE_IDX];
> > +		pmu->name = "cpu_core";
> 
> > +		/* Initialize Atom core specific PerfMon capabilities.*/
> > +		pmu = &x86_pmu.hybrid_pmu[X86_HYBRID_PMU_ATOM_IDX];
> > +		pmu->name = "cpu_atom";
> 
> So do these things use the same event lists as SPR and TNT? Is there any
> way to discover that, because AFAICT /proc/cpuinfo will say every CPU
> is 'Alderlake', and the above also doesn't give any clue.
> 
> FWIW, ARM big.LITTLE does discriminate in its /proc/cpuinfo, but I'm not
> entirely sure it's really useful. Mark said perf userspace uses
> somethink akin to our CPUID, except exposed through sysfs, to find the
> event lists.
> 
> My desktop has: cpu/caps/pmu_name and that gives "skylake", do we want
> the above to have cpu_core/caps/pmu_name give "sapphire_rapids" etc.. ?

FWIW, "Tremont" is the only pmu_name with a capital :-( I don't suppose
we can still fix that?