linux-kernel - Re: [Patch v4 09/13] perf/x86/intel: Setup PEBS data configuration and enable legacy groups

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Message-ID: <2136b1ae-6fd4-4037-95c3-3a8eb9f24e24@linux.intel.com>
Date: Mon, 23 Jun 2025 09:55:13 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo
 <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
 Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Kan Liang <kan.liang@...ux.intel.com>, Andi Kleen <ak@...ux.intel.com>,
 Eranian Stephane <eranian@...gle.com>, linux-kernel@...r.kernel.org,
 linux-perf-users@...r.kernel.org, Dapeng Mi <dapeng1.mi@...el.com>
Subject: Re: [Patch v4 09/13] perf/x86/intel: Setup PEBS data configuration
 and enable legacy groups


On 6/21/2025 5:41 PM, Peter Zijlstra wrote:
> On Fri, Jun 20, 2025 at 10:39:05AM +0000, Dapeng Mi wrote:
>
>> +static inline void __intel_pmu_update_event_ext(int idx, u64 ext)
>> +{
>> +	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
>> +	u32 msr = idx < INTEL_PMC_IDX_FIXED ?
>> +		  x86_pmu_cfg_c_addr(idx, true) :
>> +		  x86_pmu_cfg_c_addr(idx - INTEL_PMC_IDX_FIXED, false);
>> +
>> +	cpuc->cfg_c_val[idx] = ext;
>> +	wrmsrq(msr, ext);
>> +}
>> +static inline unsigned int x86_pmu_cfg_c_addr(int index, bool gp)
>> +{
>> +	u32 base = gp ? MSR_IA32_PMC_V6_GP0_CFG_C : MSR_IA32_PMC_V6_FX0_CFG_C;
>> +
>> +	return base + (x86_pmu.addr_offset ? x86_pmu.addr_offset(index, false) :
>> +					     index * MSR_IA32_PMC_V6_STEP);
>> +}
> This seems like an aweful lot of conditions just to get an ddress.
>
> Also, IIRC we have intel_pmu_v6_addr_offset() and that does: index *
> MSR_IA32_PMC_V6_STEP, so something is very redundant here.

Hmm, the intent of adding this helper is just to follow the existed helpers
like x86_pmu_event_addr(), but considering currently only
__intel_pmu_update_event_ext() need to touch the XXX_CFG_C MSRs, we may not
need to an dedicated helper. Would remove this helper.


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