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Message-ID: <96e41431-eb80-f61d-9ab9-c76cd9b6086a@amd.com>
Date:   Mon, 9 May 2022 18:38:19 +0530
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Subject: Re: [PATCH v4 3/7] perf/x86/amd/core: Detect PerfMonV2 support
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To:     Like Xu <like.xu.linux@gmail.com>
Cc:     peterz@infradead.org, bp@alien8.de, dave.hansen@linux.intel.com,
        acme@kernel.org, mark.rutland@arm.com,
        alexander.shishkin@linux.intel.com, namhyung@kernel.org,
        jolsa@kernel.org, tglx@linutronix.de, mingo@redhat.com,
        pbonzini@redhat.com, jmattson@google.com, eranian@google.com,
        puwen@hygon.cn, ananth.narayan@amd.com, ravi.bangoria@amd.com,
        santosh.shukla@amd.com,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        linux-perf-users@vger.kernel.org, x86@kernel.org
References: <cover.1651058600.git.sandipan.das@amd.com>
 <8d3e23760726cf6647a98999e1fcd12a37f36a42.1651058600.git.sandipan.das@amd.com>
 <78e001bd-42bd-5481-5a19-1a0bcca9a63c@gmail.com>
From:   Sandipan Das <sandipan.das@amd.com>
In-Reply-To: <78e001bd-42bd-5481-5a19-1a0bcca9a63c@gmail.com>
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On 5/9/2022 6:31 PM, Like Xu wrote:
> On 27/4/2022 7:31 pm, Sandipan Das wrote:
> 
>>       x86_pmu.num_counters    = AMD64_NUM_COUNTERS_CORE;
> 
> Thus boot_cpu_has(X86_FEATURE_PERFCTR_CORE) is true.
> 
>> +
>> +    /* Check for Performance Monitoring v2 support */
>> +    if (boot_cpu_has(X86_FEATURE_PERFMON_V2)) {
>> +        /* Update PMU version for later usage */
>> +        x86_pmu.version = 2;
> 
> Is it safe to assume that once AMD CPU has the PERFMON_V2 (or further) bit,
> 
> it must also have the PERFCTR_CORE bit set ?
> 

Yes, always. There won't be a case where PERFCTR_CORE is absent
but PERFMON_V2 is present.

- Sandipan