linux-kernel - Re: [RESEND][PATCH v2 0/2] perf record: ratio-to-prev event term for auto counter reload

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Message-ID: <6478744c4c07fae4b889b252248522f81359ec77.camel@intel.com>
Date: Wed, 24 Sep 2025 19:09:22 +0000
From: "Falcon, Thomas" <thomas.falcon@...el.com>
To: "alexander.shishkin@...ux.intel.com" <alexander.shishkin@...ux.intel.com>,
	"peterz@...radead.org" <peterz@...radead.org>, "acme@...nel.org"
	<acme@...nel.org>, "mingo@...hat.com" <mingo@...hat.com>,
	"mark.rutland@....com" <mark.rutland@....com>, "Hunter, Adrian"
	<adrian.hunter@...el.com>, "namhyung@...nel.org" <namhyung@...nel.org>,
	"irogers@...gle.com" <irogers@...gle.com>, "jolsa@...nel.org"
	<jolsa@...nel.org>, "kan.liang@...ux.intel.com" <kan.liang@...ux.intel.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: Re: [RESEND][PATCH v2 0/2] perf record: ratio-to-prev event term for
 auto counter reload

On Tue, 2025-09-02 at 11:40 -0500, Thomas Falcon wrote:
> The Auto Counter Reload (ACR)[1] feature is used to track the
> relative rates of two or more perf events, only sampling
> when a given threshold is exceeded. This helps reduce overhead
> and unnecessary samples. However, enabling this feature
> currently requires setting two parameters:

Ping.

Thanks,
Tom

> 
>  -- Event sampling period ("period")
>  -- acr_mask, which determines which events get reloaded
>     when the sample period is reached.
> 
> For example, in the following command:
> 
> perf record -e "{cpu_atom/branch-misses,period=200000,\
> acr_mask=0x2/ppu,cpu_atom/branch-instructions,period=1000000,\
> acr_mask=0x3/u}" -- ./mispredict
> 
> The goal is to limit event sampling to cases when the
> branch miss rate exceeds 20%. If the branch instructions
> sample period is exceeded first, both events are reloaded.
> If branch misses exceed their threshold first, only the
> second counter is reloaded, and a sample is taken.
> 
> To simplify this, provide a new “ratio-to-prev” event term
> that works alongside the period event option or -c option.
> This would allow users to specify the desired relative rate
> between events as a ratio, making configuration more intuitive.
> 
> With this enhancement, the equivalent command would be:
> 
> perf record -e "{cpu_atom/branch-misses/ppu,\
> cpu_atom/branch-instructions,period=1000000,ratio_to_prev=5/u}" \
> -- ./mispredict
> 
> or
> 
> perf record -e "{cpu_atom/branch-misses/ppu,\
> cpu_atom/branch-instructions,ratio-to-prev=5/u}" -c 1000000 \
> -- ./mispredict
> 
> [1]
> https://lore.kernel.org/lkml/20250327195217.2683619-1-kan.liang@linux.intel.com/
> 
> Changes in v2 (mostly suggested by Ian Rogers):
> 
> -- Add documentation explaining acr_mask bitmask used by ACR
> -- Move ACR specific implementation to arch/x86/
> -- Provide test cases for event parsing and perf record tests
> 
> Thomas Falcon (2):
>   perf record: Add ratio-to-prev term
>   perf record: add auto counter reload parse and regression tests
> 
>  tools/perf/Documentation/intel-acr.txt | 53 ++++++++++++++++++
>  tools/perf/Documentation/perf-list.txt |  2 +
>  tools/perf/arch/x86/util/evsel.c       | 53 ++++++++++++++++++
>  tools/perf/tests/parse-events.c        | 54 ++++++++++++++++++
>  tools/perf/tests/shell/record.sh       | 40 ++++++++++++++
>  tools/perf/util/evsel.c                | 76
> ++++++++++++++++++++++++++
>  tools/perf/util/evsel.h                |  1 +
>  tools/perf/util/evsel_config.h         |  1 +
>  tools/perf/util/parse-events.c         | 22 ++++++++
>  tools/perf/util/parse-events.h         |  3 +-
>  tools/perf/util/parse-events.l         |  1 +
>  tools/perf/util/pmu.c                  |  3 +-
>  12 files changed, 307 insertions(+), 2 deletions(-)
>  create mode 100644 tools/perf/Documentation/intel-acr.txt
>