linux-kernel - Re: [RFC/PATCH 0/4] perf tools: Do not set attr.exclude

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

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?