linux-kernel - Re: [PATCH 2/2] perf/x86/amd/core: Add ref-cycles event for Zen 4 and later

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Message-ID: <3de9ea09-5a30-4469-95b6-c752e3a485ab@amd.com>
Date: Tue, 26 Mar 2024 11:46:32 +0530
From: Sandipan Das <sandipan.das@....com>
To: Ian Rogers <irogers@...gle.com>
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
 x86@...nel.org, peterz@...radead.org, mingo@...nel.org, acme@...nel.org,
 namhyung@...nel.org, mark.rutland@....com,
 alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
 adrian.hunter@...el.com, tglx@...utronix.de, bp@...en8.de,
 eranian@...gle.com, ravi.bangoria@....com, ananth.narayan@....com
Subject: Re: [PATCH 2/2] perf/x86/amd/core: Add ref-cycles event for Zen 4 and
 later

On 3/25/2024 8:13 PM, Ian Rogers wrote:
> On Mon, Mar 25, 2024 at 12:48 AM Sandipan Das <sandipan.das@....com> wrote:
>>
>> Add the "ref-cycles" event for AMD processors based on Zen 4 and later
>> microarchitectures. The backing event is based on PMCx120 which counts
>> cycles not in halt state in P0 frequency (same as MPERF).
> 
> This reminds me that we lack smi cost and an smi_cycles metric for
> AMD, here is an Intel one:
> https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/pmu-events/arch/x86/skylakex/skx-metrics.json?h=perf-tools-next#n274
> The metric uses APERF but runs with freeze_on_smi set:
> https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/builtin-stat.c?h=perf-tools-next#n2115
> so the delta between cycles and aperf is the cycles in SMI. It would
> be great if we could get something similar on AMD.
> 

Thanks for the suggestion. I found PMCx02B ("ls_smi_rx" in perf JSONs) in
the AMD PPRs which counts the number of SMIs received but there's no way
to know how many cycles were spent in System Management Mode. I also could
not find an equivalent for the Freeze on SMI feature.

>> Signed-off-by: Sandipan Das <sandipan.das@....com>
> 
> Reviewed-by: Ian Rogers <irogers@...gle.com>
> 
> Thanks,
> Ian
> 
>> ---
>>  arch/x86/events/amd/core.c | 15 +++++++++++++++
>>  1 file changed, 15 insertions(+)
>>
>> diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
>> index afe4a809f2ed..685bfa860d67 100644
>> --- a/arch/x86/events/amd/core.c
>> +++ b/arch/x86/events/amd/core.c
>> @@ -273,8 +273,23 @@ static const u64 amd_zen2_perfmon_event_map[PERF_COUNT_HW_MAX] =
>>         [PERF_COUNT_HW_STALLED_CYCLES_FRONTEND] = 0x00a9,
>>  };
>>
>> +static const u64 amd_zen4_perfmon_event_map[PERF_COUNT_HW_MAX] =
>> +{
>> +       [PERF_COUNT_HW_CPU_CYCLES]              = 0x0076,
>> +       [PERF_COUNT_HW_INSTRUCTIONS]            = 0x00c0,
>> +       [PERF_COUNT_HW_CACHE_REFERENCES]        = 0xff60,
>> +       [PERF_COUNT_HW_CACHE_MISSES]            = 0x0964,
>> +       [PERF_COUNT_HW_BRANCH_INSTRUCTIONS]     = 0x00c2,
>> +       [PERF_COUNT_HW_BRANCH_MISSES]           = 0x00c3,
>> +       [PERF_COUNT_HW_STALLED_CYCLES_FRONTEND] = 0x00a9,
>> +       [PERF_COUNT_HW_REF_CPU_CYCLES]          = 0x100000120,
>> +};
>> +
>>  static u64 amd_pmu_event_map(int hw_event)
>>  {
>> +       if (cpu_feature_enabled(X86_FEATURE_ZEN4) || boot_cpu_data.x86 >= 0x1a)
>> +               return amd_zen4_perfmon_event_map[hw_event];
>> +
>>         if (cpu_feature_enabled(X86_FEATURE_ZEN2) || boot_cpu_data.x86 >= 0x19)
>>                 return amd_zen2_perfmon_event_map[hw_event];
>>
>> --
>> 2.34.1
>>