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

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Message-ID: <0094f13f-17b9-3d55-a57c-a48e82fb848c@linux.intel.com>
Date:   Thu, 11 Mar 2021 12:31:06 -0500
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 3/11/2021 11:32 AM, Peter Zijlstra wrote:
> 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?
> 

The cpu/caps/pmu_name is not used for the event list.

I don't think perf tool checks the "Tremont". I think it should be OK to 
fix it. Let me post a patch.

Thanks,
Kan