#
# vfsreadlat.py        VFS read latency distribution.
#            For Linux, uses BCC, eBPF. See .c file.
#
# Written as a basic example of a function latency distribution histogram.
#
# USAGE: vfsreadlat.py [interval [count]]
#
# The default interval is 5 seconds. A Ctrl-C will print the partially
# gathered histogram then exit.
#
# Copyright (c) 2015 Brendan Gregg.
# Licensed under the Apache License, Version 2.0 (the "License")
#
# 15-Aug-2015    Brendan Gregg    Created this.

from __future__ import print_function
from bcc import BPF
from ctypes import c_ushort, c_int, c_ulonglong
from time import sleep
from sys import argv

def usage():
    print("USAGE: %s [interval [count]]" % argv[0])
    exit()

# arguments
interval = 5
count = -1
if len(argv) > 1:
    try:
        interval = int(argv[1])
        if interval == 0:
            raise
        if len(argv) > 2:
            count = int(argv[2])
    except:    # also catches -h, --help
        usage()

# load BPF program
b = BPF(src_file = "vfsreadlat.c")
b.attach_kprobe(event="vfs_read", fn_name="do_entry")
b.attach_kretprobe(event="vfs_read", fn_name="do_return")

# header
print("Tracing... Hit Ctrl-C to end.")

# output
loop = 0
do_exit = 0
while (1):
    if count > 0:
        loop += 1
        if loop > count:
            exit()
    try:
        sleep(interval)
    except KeyboardInterrupt:
        pass; do_exit = 1

    print()
    b["dist"].print_log2_hist("usecs")
    b["dist"].clear()
    if do_exit:
        exit()