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Date: Mon, 2 Sep 2024 10:56:28 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Namhyung Kim <namhyung@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>,
	Ian Rogers <irogers@google.com>,
	Kan Liang <kan.liang@linux.intel.com>, Jiri Olsa <jolsa@kernel.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Ingo Molnar <mingo@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
	linux-perf-users@vger.kernel.org,
	Ravi Bangoria <ravi.bangoria@amd.com>,
	Mark Rutland <mark.rutland@arm.com>,
	James Clark <james.clark@arm.com>,
	Athira Rajeev <atrajeev@linux.vnet.ibm.com>,
	Kajol Jain <kjain@linux.ibm.com>,
	Thomas Richter <tmricht@linux.ibm.com>,
	Atish Patra <atishp@atishpatra.org>,
	Palmer Dabbelt <palmer@rivosinc.com>,
	Mingwei Zhang <mizhang@google.com>
Subject: Re: [RFC/PATCH 0/4] perf tools: Do not set attr.exclude_guest by
 default (v1)
Message-ID: <20240902085628.GA4723@noisy.programming.kicks-ass.net>
References: <20240902014621.2002343-1-namhyung@kernel.org>
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In-Reply-To: <20240902014621.2002343-1-namhyung@kernel.org>

On Sun, Sep 01, 2024 at 06:46:17PM -0700, Namhyung Kim wrote:
> Hello,
> 
> I found perf tools set exclude_guest bit inconsistently.  It used to
> set the bit but now the default event for perf record doesn't.  So I'm
> wondering why we want the bit in the first place.
> 
> Actually it's not good for PMUs don't support any exclusion like AMD
> IBS because it disables new features after the exclude_guest due to
> the missing feature detection logic.
> 
> AFAIK it doesn't matter for the most cases but perf kvm.  If users
> need to set the bit, they can still use :H modifier.  Please let me
> know if it's ok for you.

IIRc the point of setting exclude_guest by default was so that default
perf keeps working in the precense of that PMU pass through mess, no?