linux-kernel - Re: [Patch v3 0/2] perf record: ratio-to-prev event term for auto counter reload

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Message-ID: <1cd532e63acc22a4c6632285195305972ae36122.camel@intel.com>
Date: Mon, 6 Oct 2025 16:23:42 +0000
From: "Falcon, Thomas" <thomas.falcon@...el.com>
To: "acme@...nel.org" <acme@...nel.org>
CC: "alexander.shishkin@...ux.intel.com" <alexander.shishkin@...ux.intel.com>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-perf-users@...r.kernel.org"
	<linux-perf-users@...r.kernel.org>, "peterz@...radead.org"
	<peterz@...radead.org>, "mark.rutland@....com" <mark.rutland@....com>,
	"mingo@...hat.com" <mingo@...hat.com>, "Hunter, Adrian"
	<adrian.hunter@...el.com>, "namhyung@...nel.org" <namhyung@...nel.org>,
	"jolsa@...nel.org" <jolsa@...nel.org>, "kan.liang@...ux.intel.com"
	<kan.liang@...ux.intel.com>, "irogers@...gle.com" <irogers@...gle.com>,
	"dapeng1.mi@...ux.intel.com" <dapeng1.mi@...ux.intel.com>
Subject: Re: [Patch v3 0/2] perf record: ratio-to-prev event term for auto
 counter reload

On Fri, 2025-10-03 at 16:27 -0300, Arnaldo Carvalho de Melo wrote:
> On Thu, Oct 02, 2025 at 06:43:04PM -0500,
> thomas.falcon@...el.com wrote:
> > 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/
> > v3: rebase to current perf-tools-next
> 
> Thanks, applied to perf-tools-next,
> 
> - Arnaldo
>  

Thank you and thanks to Ian and everyone else that took their time to
review.

Thanks,
Tom

> > v2: (changes below suggested by Ian Rogers):
>