linux-kernel - Re: [PATCH v4 4/9] libperf: Add libperf_evsel_

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Message-ID: <20201014110527.GA1349644@krava>
Date:   Wed, 14 Oct 2020 13:05:27 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Raphael Gault <raphael.gault@....com>,
        Mark Rutland <mark.rutland@....com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Ian Rogers <irogers@...gle.com>, honnappa.nagarahalli@....com,
        Itaru Kitayama <itaru.kitayama@...il.com>
Subject: Re: [PATCH v4 4/9] libperf: Add libperf_evsel__mmap()

On Thu, Oct 01, 2020 at 09:01:11AM -0500, Rob Herring wrote:

SNIP

>  
> +void *perf_evsel__mmap(struct perf_evsel *evsel, int pages)
> +{
> +	int ret;
> +	struct perf_mmap *map;
> +	struct perf_mmap_param mp = {
> +		.prot = PROT_READ | PROT_WRITE,
> +	};
> +
> +	if (FD(evsel, 0, 0) < 0)
> +		return NULL;
> +
> +	mp.mask = (pages * page_size) - 1;
> +
> +	map = zalloc(sizeof(*map));
> +	if (!map)
> +		return NULL;
> +
> +	perf_mmap__init(map, NULL, false, NULL);
> +
> +	ret = perf_mmap__mmap(map, &mp, FD(evsel, 0, 0), 0);

hum, so you map event for FD(0,0) but later in perf_evsel__read
you allow to read any cpu/thread combination ending up reading
data from FD(0,0) map:

	int perf_evsel__read(struct perf_evsel *evsel, int cpu, int thread,
			     struct perf_counts_values *count)
	{
		size_t size = perf_evsel__read_size(evsel);

		memset(count, 0, sizeof(*count));

		if (FD(evsel, cpu, thread) < 0)
			return -EINVAL;

		if (evsel->mmap && !perf_mmap__read_self(evsel->mmap, count))
			return 0;


I think we should either check cpu == 0, thread == 0, or make it
general and store perf_evsel::mmap in xyarray as we do for fds

thanks,
jirka