netdev - Re: [PATCH bpf-next 4/5] samples/bpf: switch trace_output sample to perf

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Date:   Tue, 23 Jul 2019 09:29:55 +0000
From:   Song Liu <songliubraving@...com>
To:     Andrii Nakryiko <andriin@...com>
CC:     bpf <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "andrii.nakryiko@...il.com" <andrii.nakryiko@...il.com>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf-next 4/5] samples/bpf: switch trace_output sample to
 perf_buffer API



> On Jul 22, 2019, at 9:31 PM, Andrii Nakryiko <andriin@...com> wrote:
> 
> Convert trace_output sample to libbpf's perf_buffer API.
> 
> Signed-off-by: Andrii Nakryiko <andriin@...com>

Acked-by: Song Liu <songliubraving@...com>

> ---
> samples/bpf/trace_output_user.c | 43 +++++++++++----------------------
> 1 file changed, 14 insertions(+), 29 deletions(-)
> 
> diff --git a/samples/bpf/trace_output_user.c b/samples/bpf/trace_output_user.c
> index 2dd1d39b152a..8ee47699a870 100644
> --- a/samples/bpf/trace_output_user.c
> +++ b/samples/bpf/trace_output_user.c
> @@ -18,9 +18,6 @@
> #include <libbpf.h>
> #include "bpf_load.h"
> #include "perf-sys.h"
> -#include "trace_helpers.h"
> -
> -static int pmu_fd;
> 
> static __u64 time_get_ns(void)
> {
> @@ -31,12 +28,12 @@ static __u64 time_get_ns(void)
> }
> 
> static __u64 start_time;
> +static __u64 cnt;
> 
> #define MAX_CNT 100000ll
> 
> -static int print_bpf_output(void *data, int size)
> +static void print_bpf_output(void *ctx, int cpu, void *data, __u32 size)
> {
> -	static __u64 cnt;
> 	struct {
> 		__u64 pid;
> 		__u64 cookie;
> @@ -45,7 +42,7 @@ static int print_bpf_output(void *data, int size)
> 	if (e->cookie != 0x12345678) {
> 		printf("BUG pid %llx cookie %llx sized %d\n",
> 		       e->pid, e->cookie, size);
> -		return LIBBPF_PERF_EVENT_ERROR;
> +		return;
> 	}
> 
> 	cnt++;
> @@ -53,30 +50,14 @@ static int print_bpf_output(void *data, int size)
> 	if (cnt == MAX_CNT) {
> 		printf("recv %lld events per sec\n",
> 		       MAX_CNT * 1000000000ll / (time_get_ns() - start_time));
> -		return LIBBPF_PERF_EVENT_DONE;
> +		return;
> 	}
> -
> -	return LIBBPF_PERF_EVENT_CONT;
> -}
> -
> -static void test_bpf_perf_event(void)
> -{
> -	struct perf_event_attr attr = {
> -		.sample_type = PERF_SAMPLE_RAW,
> -		.type = PERF_TYPE_SOFTWARE,
> -		.config = PERF_COUNT_SW_BPF_OUTPUT,
> -	};
> -	int key = 0;
> -
> -	pmu_fd = sys_perf_event_open(&attr, -1/*pid*/, 0/*cpu*/, -1/*group_fd*/, 0);
> -
> -	assert(pmu_fd >= 0);
> -	assert(bpf_map_update_elem(map_fd[0], &key, &pmu_fd, BPF_ANY) == 0);
> -	ioctl(pmu_fd, PERF_EVENT_IOC_ENABLE, 0);
> }
> 
> int main(int argc, char **argv)
> {
> +	struct perf_buffer_opts pb_opts = {};
> +	struct perf_buffer *pb;
> 	char filename[256];
> 	FILE *f;
> 	int ret;
> @@ -88,16 +69,20 @@ int main(int argc, char **argv)
> 		return 1;
> 	}
> 
> -	test_bpf_perf_event();
> -
> -	if (perf_event_mmap(pmu_fd) < 0)
> +	pb_opts.sample_cb = print_bpf_output;
> +	pb = perf_buffer__new(map_fd[0], 8, &pb_opts);
> +	ret = libbpf_get_error(pb);
> +	if (ret) {
> +		printf("failed to setup perf_buffer: %d\n", ret);
> 		return 1;
> +	}
> 
> 	f = popen("taskset 1 dd if=/dev/zero of=/dev/null", "r");
> 	(void) f;
> 
> 	start_time = time_get_ns();
> -	ret = perf_event_poller(pmu_fd, print_bpf_output);
> +	while ((ret = perf_buffer__poll(pb, 1000)) >= 0 && cnt < MAX_CNT) {
> +	}
> 	kill(0, SIGINT);
> 	return ret;
> }
> -- 
> 2.17.1
>