samples/bpf: add perf_event+bpf example

The bpf program is called 50 times a second and does hashmap[kern&user_stackid]++
It's primary purpose to check that key bpf helpers like map lookup, update,
get_stackid, trace_printk and ctx access are all working.
It checks:
- PERF_COUNT_HW_CPU_CYCLES on all cpus
- PERF_COUNT_HW_CPU_CYCLES for current process and inherited perf_events to children
- PERF_COUNT_SW_CPU_CLOCK on all cpus
- PERF_COUNT_SW_CPU_CLOCK for current process

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 65 insertions, 0 deletions

diff --git a/samples/bpf/trace_event_kern.c b/samples/bpf/trace_event_kern.c
new file mode 100644
index 0000000..71a8ed3
--- /dev/null
+++ b/samples/bpf/trace_event_kern.c
@@ -0,0 +1,65 @@
+/* Copyright (c) 2016 Facebook
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+#include <linux/ptrace.h>
+#include <linux/version.h>
+#include <uapi/linux/bpf.h>
+#include <uapi/linux/bpf_perf_event.h>
+#include <uapi/linux/perf_event.h>
+#include "bpf_helpers.h"
+
+struct key_t {
+	char comm[TASK_COMM_LEN];
+	u32 kernstack;
+	u32 userstack;
+};
+
+struct bpf_map_def SEC("maps") counts = {
+	.type = BPF_MAP_TYPE_HASH,
+	.key_size = sizeof(struct key_t),
+	.value_size = sizeof(u64),
+	.max_entries = 10000,
+};
+
+struct bpf_map_def SEC("maps") stackmap = {
+	.type = BPF_MAP_TYPE_STACK_TRACE,
+	.key_size = sizeof(u32),
+	.value_size = PERF_MAX_STACK_DEPTH * sizeof(u64),
+	.max_entries = 10000,
+};
+
+#define KERN_STACKID_FLAGS (0 | BPF_F_FAST_STACK_CMP)
+#define USER_STACKID_FLAGS (0 | BPF_F_FAST_STACK_CMP | BPF_F_USER_STACK)
+
+SEC("perf_event")
+int bpf_prog1(struct bpf_perf_event_data *ctx)
+{
+	char fmt[] = "CPU-%d period %lld ip %llx";
+	u32 cpu = bpf_get_smp_processor_id();
+	struct key_t key;
+	u64 *val, one = 1;
+
+	if (ctx->sample_period < 10000)
+		/* ignore warmup */
+		return 0;
+	bpf_get_current_comm(&key.comm, sizeof(key.comm));
+	key.kernstack = bpf_get_stackid(ctx, &stackmap, KERN_STACKID_FLAGS);
+	key.userstack = bpf_get_stackid(ctx, &stackmap, USER_STACKID_FLAGS);
+	if ((int)key.kernstack < 0 && (int)key.userstack < 0) {
+		bpf_trace_printk(fmt, sizeof(fmt), cpu, ctx->sample_period,
+				 ctx->regs.ip);
+		return 0;
+	}
+
+	val = bpf_map_lookup_elem(&counts, &key);
+	if (val)
+		(*val)++;
+	else
+		bpf_map_update_elem(&counts, &key, &one, BPF_NOEXIST);
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";