linux-kernel - Re: [PATCH v2 5/5] perf metric: Don't compute unused events.

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Message-ID: <20201119205920.GM1475102@krava>
Date:   Thu, 19 Nov 2020 21:59:20 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
        Jin Yao <yao.jin@...ux.intel.com>,
        John Garry <john.garry@...wei.com>,
        Paul Clarke <pc@...ibm.com>, kajoljain <kjain@...ux.ibm.com>,
        Stephane Eranian <eranian@...gle.com>,
        Sandeep Dasgupta <sdasgup@...gle.com>,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v2 5/5] perf metric: Don't compute unused events.

On Tue, Nov 17, 2020 at 09:03:35PM -0800, Ian Rogers wrote:

SNIP

> +			ids__free($1.ids);
> +			ids__free($3.ids);
> +		}
> +	} else {
> +		$$.val = NAN;
> +		$$.ids = ids__union($1.ids, $3.ids);
> +	}
> +}
> +| expr '*' expr
> +{
> +	if (!compute_ids || (isfinite($1.val) && isfinite($3.val))) {
> +		$$.val = $1.val * $3.val;
> +		$$.ids = NULL;
> +		if (compute_ids) {
> +			ids__free($1.ids);
> +			ids__free($3.ids);
> +		}
> +	} else {
> +		$$.val = NAN;
> +		$$.ids = ids__union($1.ids, $3.ids);
> +	}
> +}
> +| expr '/' expr
> +{
> +	if (fpclassify($3.val) == FP_ZERO) {
> +		pr_debug("division by zero\n");
> +		YYABORT;
> +	} else if (!compute_ids || (isfinite($1.val) && isfinite($3.val))) {
> +		$$.val = $1.val / $3.val;
> +		$$.ids = NULL;

hum, I'm confused with this.. compute_ids with finite values?
why do we erase ids then? also val should be NAN then, no?
could you please put in some comment with reasoning?

thanks,
jirka