linux-kernel - Re: [PATCH v4 04/38] perf: Add a EVENT

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Message-ID: <def6a396-b6c0-4b7a-8ccd-6d4a0a8f6aaa@linux.intel.com>
Date: Thu, 15 May 2025 09:35:30 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>,
 Mingwei Zhang <mizhang@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>,
 Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
 Adrian Hunter <adrian.hunter@...el.com>, Liang@...gle.com,
 Kan <kan.liang@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>,
 linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
 Yongwei Ma <yongwei.ma@...el.com>,
 Xiong Zhang <xiong.y.zhang@...ux.intel.com>,
 Jim Mattson <jmattson@...gle.com>, Sandipan Das <sandipan.das@....com>,
 Zide Chen <zide.chen@...el.com>, Eranian Stephane <eranian@...gle.com>,
 Shukla Manali <Manali.Shukla@....com>,
 Nikunj Dadhania <nikunj.dadhania@....com>
Subject: Re: [PATCH v4 04/38] perf: Add a EVENT_GUEST flag

On 5/15/2025 6:51 AM, Sean Christopherson wrote:
> On Mon, Mar 24, 2025, Mingwei Zhang wrote:
>> +{
>> +	if (event->attr.exclude_guest && __this_cpu_read(perf_in_guest)) {
> My vote is for s/perf_in_guest/guest_ctx_loaded, because "perf in guest" doesn't
> accurately describe just the mediated PMU case.  E.g. perf itself is running in
> KVM guests when using an emulated vPMU, or no vPMU at all.

Agree.

>
> And with a Kconfig to guard the mediated PMU, this check (and others) can be
> elided at compile time for architectures that don't support a mediated PMU (or
> if KVM is disabled).
>
>> +		/*
>> +		 * (now + times[total].offset) - (now + times[guest].offset) :=
>> +		 * times[total].offset - times[guest].offset
>> +		 */
>> +		return READ_ONCE(times[T_TOTAL].offset) - READ_ONCE(times[T_GUEST].offset);
>> +	}
>> +
>> +	return now + READ_ONCE(times[T_TOTAL].offset);
>> +}
>> +