linux-kernel - Re: [PATCH v4 4/4] samples/bpf: example of get selected PMU counter value

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Date:	Thu, 30 Jul 2015 01:56:41 +0200
From:	Daniel Borkmann <daniel@...earbox.net>
To:	Kaixu Xia <xiakaixu@...wei.com>, ast@...mgrid.com,
	davem@...emloft.net, acme@...nel.org, mingo@...hat.com,
	a.p.zijlstra@...llo.nl, masami.hiramatsu.pt@...achi.com,
	jolsa@...nel.org
CC:	wangnan0@...wei.com, linux-kernel@...r.kernel.org,
	pi3orama@....com, hekuang@...wei.com
Subject: Re: [PATCH v4 4/4] samples/bpf: example of get selected PMU counter
 value

On 07/28/2015 01:17 PM, Kaixu Xia wrote:
> This is a simple example and shows how to use the new ability
> to get the selected Hardware PMU counter value.
>
> Signed-off-by: Kaixu Xia <xiakaixu@...wei.com>
...
> diff --git a/samples/bpf/tracex6_user.c b/samples/bpf/tracex6_user.c
> new file mode 100644
> index 0000000..e607eac
> --- /dev/null
> +++ b/samples/bpf/tracex6_user.c
> @@ -0,0 +1,67 @@
> +#include <stdio.h>
> +#include <unistd.h>
> +#include <stdlib.h>
> +#include <stdbool.h>
> +#include <string.h>
> +#include <fcntl.h>
> +#include <poll.h>
> +#include <sys/ioctl.h>
> +#include <linux/perf_event.h>
> +#include <linux/bpf.h>
> +#include "libbpf.h"
> +#include "bpf_load.h"
> +
> +static void test_bpf_perf_event(void)
> +{
> +	int nr_cpus = sysconf(_SC_NPROCESSORS_CONF);
> +	int *pmu_fd = malloc(nr_cpus * sizeof(int));
> +	unsigned long value;
> +	int i;
> +
> +	struct perf_event_attr attr_insn_pmu = {
> +		.freq = 0,
> +		.sample_period = 0x7fffffffffffffffULL,

Nit: #define ...

> +		.inherit = 0,
> +		.type = PERF_TYPE_HARDWARE,
> +		.read_format = 0,
> +		.sample_type = 0,
> +		.config = 0,/* PMU: cycles */
> +	};
> +
> +	for (i = 0; i < nr_cpus; i++) {
> +		pmu_fd[i] = perf_event_open(&attr_insn_pmu, -1/*pid*/, i/*cpu*/, -1/*group_fd*/, 0);
> +		if (pmu_fd[i] < 0)
> +			printf("event syscall failed\n");
> +
> +		bpf_update_elem(map_fd[0], &i, (pmu_fd + i), BPF_ANY);

Nit: you use pmu_fd[i], but here (pmu_fd + i)? Maybe better &pmu_fd[i]?

> +		ioctl(pmu_fd[i], PERF_EVENT_IOC_ENABLE, 0);
> +	}
--
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