Example for using BPF perf event

tools/llcstat.py

+#!/usr/bin/python
+#
+# llcstat.py Summarize cache references and cache misses by PID.
+#            Cache reference and cache miss are corresponding events defined in
+#            uapi/linux/perf_event.h, it varies to different architecture.
+#            On x86-64, they mean LLC references and LLC misses.
+#
+#            For Linux, uses BCC, eBPF. Embedded C.
+#
+# REQUIRES: Linux 4.9+ (BPF_PROG_TYPE_PERF_EVENT support).
+#
+# Copyright (c) 2016 Facebook, Inc.
+# Licensed under the Apache License, Version 2.0 (the "License")
+#
+# 19-Oct-2016   Teng Qin   Created this.
+
+from __future__ import print_function
+import argparse
+from bcc import BPF, PerfType, PerfHWConfig
+import signal
+from time import sleep
+
+parser = argparse.ArgumentParser(
+    description="Summarize cache references and misses by PID",
+    formatter_class=argparse.RawDescriptionHelpFormatter)
+parser.add_argument(
+    "-c", "--sample_period", type=int, default=100,
+    help="Sample one in this many number of cache reference / miss events")
+parser.add_argument(
+    "duration", nargs="?", default=10, help="Duration, in seconds, to run")
+args = parser.parse_args()
+
+# load BPF program
+b = BPF(text="""
+#include <linux/ptrace.h>
+#include <uapi/linux/bpf_perf_event.h>
+
+struct key_t {
+    int cpu;
+    int pid;
+    char name[TASK_COMM_LEN];
+};
+
+BPF_HASH(ref_count, struct key_t);
+BPF_HASH(miss_count, struct key_t);
+
+static inline __attribute__((always_inline)) void get_key(struct key_t* key) {
+    key->cpu = bpf_get_smp_processor_id();
+    key->pid = bpf_get_current_pid_tgid();
+    bpf_get_current_comm(&(key->name), sizeof(key->name));
+}
+
+int on_cache_miss(struct bpf_perf_event_data *ctx) {
+    struct key_t key = {};
+    get_key(&key);
+
+    u64 zero = 0, *val;
+    val = miss_count.lookup_or_init(&key, &zero);
+    (*val) += ctx->sample_period;
+
+    return 0;
+}
+
+int on_cache_ref(struct bpf_perf_event_data *ctx) {
+    struct key_t key = {};
+    get_key(&key);
+
+    u64 zero = 0, *val;
+    val = ref_count.lookup_or_init(&key, &zero);
+    (*val) += ctx->sample_period;
+
+    return 0;
+}
+""")
+
+b.attach_perf_event(
+    ev_type=PerfType.HARDWARE, ev_config=PerfHWConfig.CACHE_MISSES,
+    fn_name="on_cache_miss", sample_period=args.sample_period)
+b.attach_perf_event(
+    ev_type=PerfType.HARDWARE, ev_config=PerfHWConfig.CACHE_REFERENCES,
+    fn_name="on_cache_ref", sample_period=args.sample_period)
+
+print("Running for {} seconds or hit Ctrl-C to end.".format(args.duration))
+
+try:
+    sleep(float(args.duration))
+except KeyboardInterrupt:
+    signal.signal(signal.SIGINT, lambda signal, frame: print())
+
+miss_count = {}
+for (k, v) in b.get_table('miss_count').items():
+    miss_count[(k.pid, k.cpu, k.name)] = v.value
+
+print('PID      NAME             CPU     REFERENCE         MISS    HIT%')
+tot_ref = 0
+tot_miss = 0
+for (k, v) in b.get_table('ref_count').items():
+    try:
+        miss = miss_count[(k.pid, k.cpu, k.name)]
+    except KeyError:
+        miss = 0
+    tot_ref += v.value
+    tot_miss += miss
+    # This happens on some PIDs due to missed counts caused by sampling
+    hit = (v.value - miss) if (v.value >= miss) else 0
+    print('{:<8d} {:<16s} {:<4d} {:>12d} {:>12d} {:>6.2f}%'.format(
+        k.pid, k.name, k.cpu, v.value, miss,
+        (float(hit) / float(v.value)) * 100.0))
+print('Total References: {} Total Misses: {} Hit Rate: {:.2f}%'.format(
+    tot_ref, tot_miss, (float(tot_ref - tot_miss) / float(tot_ref)) * 100.0))