linux-kernel - Re: [RFCv2 4/4] perf: util: support sysfs supported

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Message-ID: <c6eff854-c415-4024-5134-1d8af7006d98@arm.com>
Date:	Mon, 18 Jul 2016 17:38:16 +0100
From:	Suzuki K Poulose <Suzuki.Poulose@....com>
To:	Mark Rutland <mark.rutland@....com>, linux-kernel@...r.kernel.org
Cc:	acme@...nel.org, adrian.hunter@...el.com,
	alexander.shishkin@...ux.intel.com, hekuang@...wei.com,
	jolsa@...nel.org, kan.liang@...el.com, mingo@...hat.com,
	peterz@...radead.org, wangnan0@...wei.com
Subject: Re: [RFCv2 4/4] perf: util: support sysfs supported_cpumask file

On 15/07/16 11:08, Mark Rutland wrote:
> For system PMUs, the perf tools have long expected a cpumask file under
> sysfs, describing the single CPU which they support events being
> opened/handled on. Prior patches in this series have reworked this
> support to support multiple CPUs in a mask, as is required to handle
> heterogeneous CPU PMUs.
>
> Unfortunately, adding a cpumask file to CPU PMUs would break existing
> userspace. Prior to this series, perf record will refuse to open events,
> and perf stat may unexpectedly block at exit time. In the absence of a
> cpumask, perf stat is functional.
>
> To address this, this patch adds support for a new file,
> supported_cpumask, which can be used to describe heterogeneous CPUs,
> without the risk of breaking existing userspace binaries.
>
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> ---
>  tools/perf/util/pmu.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
> index ddb0261..06c985c 100644
> --- a/tools/perf/util/pmu.c
> +++ b/tools/perf/util/pmu.c
> @@ -445,14 +445,23 @@ static struct cpu_map *pmu_cpumask(const char *name)
>  	FILE *file;
>  	struct cpu_map *cpus;
>  	const char *sysfs = sysfs__mountpoint();
> +	const char *path_template[] = {
> +		 "%s/bus/event_source/devices/%s/cpumask",
> +		 "%s/bus/event_source/devices/%s/supported_cpumask",
> +		 NULL
> +	};
> +	unsigned int i;
>
>  	if (!sysfs)
>  		return NULL;
>
> -	snprintf(path, PATH_MAX,
> -		 "%s/bus/event_source/devices/%s/cpumask", sysfs, name);
> +	for (i = 0; i < ARRAY_SIZE(path_template); i++) {

The check could be "path_template[i]" to avoid an iteration with NULL
template.

> +		snprintf(path, PATH_MAX, *path_template, sysfs, name);

Btw, did you mean to use path_template[i] here instead of *path_template ?

> +		if (stat(path, &st) == 0)
> +			break;
> +	}
>
> -	if (stat(path, &st) < 0)
> +	if (!*path_template)

Same here ?

>  		return NULL;

Suzuki