disklatency.py

disklatency.py

#!/usr/bin/python
# 2019 by Cyrus

from __future__ import print_function
from bcc import BPF
from time import sleep

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

BPF_HASH(start, struct request *);

BPF_HISTOGRAM(dist);
BPF_HISTOGRAM(dist_linear);

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;
		dist.increment(bpf_log2l(delta / 1000000));
		dist_linear.increment(delta / 1000000);
		start.delete(&req);
	}
}

""")

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")

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

# trace until Ctrl-C
try:
	sleep(99999999)
except KeyboardInterrupt:
	print()

# output
print("log2 histogram")
print("~~~~~~~~~~~~~~")
b["dist"].print_log2_hist("time(ms)")

print("\nlinear histogram")
print("~~~~~~~~~~~~~~~~")
b["dist_linear"].print_linear_hist("time(ms)")

You need to first determine whether there is a write request to open the hard disk IO block，like this(line 39):

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