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

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Message-ID: <YEpAtTttSxMVDWYp@hirez.programming.kicks-ass.net>
Date:   Thu, 11 Mar 2021 17:09:25 +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 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.. ?