disklatency.py

#!/usr/bin/python
#
# disksnoop.py	Trace block device I/O: basic version of iosnoop.
#		For Linux, uses BCC, eBPF. Embedded C.
#
# Written as a basic example of tracing latency.
#
# Copyright (c) 2015 Brendan Gregg.
# Licensed under the Apache License, Version 2.0 (the "License")
#
# 11-Aug-2015	Brendan Gregg	Created this.

from __future__ import print_function
from bcc import BPF
from bcc.utils import printb
from time import sleep

REQ_WRITE = 1		# from include/linux/blk_types.h

# load BPF program
b = BPF(text="""
#include <uapi/linux/ptrace.h>
#include <linux/blkdev.h>

BPF_HISTOGRAM(hist);
BPF_HASH(start, struct request*);

void trace_start(struct pt_regs *ctx, struct request *req) {
	// stash start timestamp by request ptr
	u64 ts = bpf_ktime_get_ns();
	start.update(&req, &ts);
}

void trace_completion(struct pt_regs *ctx, struct request *req) {
	u64 *tsp, delta;

	tsp = start.lookup(&req);
	if (tsp != 0) {
		delta = bpf_ktime_get_ns() - *tsp;
                hist.increment(bpf_log2l(delta / 1000));
		start.delete(&req);
	}
}
""")

if BPF.get_kprobe_functions(b'blk_start_request'):
        b.attach_kprobe(event="blk_start_request", fn_name="trace_start")
b.attach_kprobe(event="blk_mq_start_request", fn_name="trace_start")
b.attach_kprobe(event="blk_account_io_completion", fn_name="trace_completion")

try:
    print("Tracing Disk Latency ... Ctrl-C end")
    sleep(9999999)
except KeyboardInterrupt:
    print()

b["hist"].print_log2_hist("Disk Latency (us)")
b["hist"].clear()