linux-kernel - Re: [RESEND PATCH] perf/x86/intel: Fix unchecked MSR access error for Alder Lake N

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Date:   Mon, 22 Aug 2022 09:24:57 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     acme@...hat.com, linux-kernel@...r.kernel.org,
        alexander.shishkin@...ux.intel.com, ak@...ux.intel.com,
        Jianfeng Gao <jianfeng.gao@...el.com>,
        Zhengjun Xing <zhengjun.xing@...ux.intel.com>
Subject: Re: [RESEND PATCH] perf/x86/intel: Fix unchecked MSR access error for
 Alder Lake N



On 2022-08-19 4:33 a.m., Peter Zijlstra wrote:
> On Fri, Aug 19, 2022 at 10:05:40AM +0200, Peter Zijlstra wrote:
>> On Thu, Aug 18, 2022 at 11:15:30AM -0700, kan.liang@...ux.intel.com wrote:
>>
>>> The Alder Lake N only has e-cores. The X86_FEATURE_HYBRID_CPU flag is
>>> not set. The perf cannot retrieve the correct CPU type via
>>> get_this_hybrid_cpu_type(). The model specific get_hybrid_cpu_type() is
>>> hardcode to p-core. The wrong CPU type is given to the PMU of the
>>> Alder Lake N.
>>
>> If ADL-N isn't in fact a hybrid CPU, then *WHY* are we running
>> init_hybrid_pmu() and setting up all that nonsense?
>>
>> That is, wouldn't the right thing be to remove ALDERLAKE_N from the rest
>> of {ALDER,RAPTOP}LAKE and create a non-hybrid PMU setup for it?
>

I think the only issue should be the PMU name. The non-hybrid PMU name
is "cpu". The hybrid PMU name is "cpu_$coretype". If we move the
ALDERLAKE_N to the non-hybrid PMU, the PMU name will be changed from
"cpu_atom" to "cpu". It will be different from the rest of
{ALDER,RAPTOP}LAKE.

Also, I think we have to update the perf tool for the events because of
the PMU name change.

But I guess it should be OK, since the ALDERLAKE_N was just added and we
know its an Atom-only system.


> Something like the *completely* untested below.. which adds it like a
> regular atom chip (which it is).

I will do more tests and send out a V2.

Thanks,
Kan
> 
> (I basically did copy/paste of tremont and added bits from the cpu_atom
> thing from alderlake -- but might well have missed something)
> 
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 2db93498ff71..e509f1033a2d 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -5974,6 +5974,38 @@ __init int intel_pmu_init(void)
>  		name = "Tremont";
>  		break;
>  
> +	case INTEL_FAM6_ALDERLAKE_N:
> +		x86_pmu.mid_ack = true;
> +		memcpy(hw_cache_event_ids, glp_hw_cache_event_ids,
> +		       sizeof(hw_cache_event_ids));
> +		memcpy(hw_cache_extra_regs, tnt_hw_cache_extra_regs,
> +		       sizeof(hw_cache_extra_regs));
> +		hw_cache_event_ids[C(ITLB)][C(OP_READ)][C(RESULT_ACCESS)] = -1;
> +
> +		intel_pmu_lbr_init_skl();
> +
> +		x86_pmu.event_constraints = intel_slm_event_constraints;
> +		x86_pmu.pebs_constraints = intel_grt_pebs_event_constraints;
> +		x86_pmu.extra_regs = intel_grt_extra_regs;
> +		/*
> +		 * It's recommended to use CPU_CLK_UNHALTED.CORE_P + NPEBS
> +		 * for precise cycles.
> +		 */
> +		x86_pmu.pebs_aliases = NULL;
> +		x86_pmu.pebs_prec_dist = true;
> +		x86_pmu.lbr_pt_coexist = true;
> +		x86_pmu.flags |= PMU_FL_HAS_RSP_1;
> +		x86_pmu.flags |= PMU_FL_NO_HT_SHARING;
> +		x86_pmu.flags |= PMU_FL_PEBS_ALL;
> +		x86_pmu.flags |= PMU_FL_INSTR_LATENCY;
> +		x86_pmu.flags |= PMU_FL_MEM_LOADS_AUX;
> +		x86_pmu.get_event_constraints = tnt_get_event_constraints;
> +		td_attr = tnt_events_attrs;
> +		extra_attr = slm_format_attr;
> +		pr_cont("Gracemont events, ");
> +		name = "Gracemont";
> +		break;
> +
>  	case INTEL_FAM6_WESTMERE:
>  	case INTEL_FAM6_WESTMERE_EP:
>  	case INTEL_FAM6_WESTMERE_EX:
> @@ -6318,7 +6350,6 @@ __init int intel_pmu_init(void)
>  
>  	case INTEL_FAM6_ALDERLAKE:
>  	case INTEL_FAM6_ALDERLAKE_L:
> -	case INTEL_FAM6_ALDERLAKE_N:
>  	case INTEL_FAM6_RAPTORLAKE:
>  	case INTEL_FAM6_RAPTORLAKE_P:
>  		/*