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# @lint-avoid-python-3-compatibility-imports
# fileslower Trace slow synchronous file reads and writes.
# For Linux, uses BCC, eBPF.
# USAGE: fileslower [-h] [-p PID] [-a] [min_ms]
# This script uses kernel dynamic tracing of synchronous reads and writes
# at the VFS interface, to identify slow file reads and writes for any file
# system.
# This works by tracing __vfs_read() and __vfs_write(), and filtering for
# synchronous I/O (the path to new_sync_read() and new_sync_write()), and
# for I/O with filenames. This approach provides a view of just two file
# system request types. There are typically many others: asynchronous I/O,
# directory operations, file handle operations, etc, that this tool does not
# instrument.
# WARNING: This traces VFS reads and writes, which can be extremely frequent,
# and so the overhead of this tool can become severe depending on the
# workload.
# By default, a minimum millisecond threshold of 10 is used.
# Copyright 2016 Netflix, Inc.
# Licensed under the Apache License, Version 2.0 (the "License")
# 06-Feb-2016 Brendan Gregg Created this.
from __future__ import print_function
from bcc import BPF
import argparse
import time
# arguments
examples = """examples:
./fileslower # trace sync file I/O slower than 10 ms (default)
./fileslower 1 # trace sync file I/O slower than 1 ms
./fileslower -p 185 # trace PID 185 only
parser = argparse.ArgumentParser(
description="Trace slow synchronous file reads and writes",
parser.add_argument("-p", "--pid", type=int, metavar="PID", dest="tgid",
help="trace this PID only")
parser.add_argument("-a", "--all-files", action="store_true",
help="include non-regular file types (sockets, FIFOs, etc)")
parser.add_argument("min_ms", nargs="?", default='10',
help="minimum I/O duration to trace, in ms (default 10)")
parser.add_argument("--ebpf", action="store_true",
args = parser.parse_args()
min_ms = int(args.min_ms)
tgid = args.tgid
debug = 0
# define BPF program
bpf_text = """
#include <uapi/linux/ptrace.h>
#include <linux/fs.h>
#include <linux/sched.h>
enum trace_mode {
struct val_t {
u32 sz;
u64 ts;
u32 name_len;
// de-> may point to de->d_iname so limit len accordingly
char name[DNAME_INLINE_LEN];
char comm[TASK_COMM_LEN];
struct data_t {
enum trace_mode mode;
u32 pid;
u32 sz;
u64 delta_us;
u32 name_len;
char name[DNAME_INLINE_LEN];
char comm[TASK_COMM_LEN];
BPF_HASH(entryinfo, pid_t, struct val_t);
// store timestamp and size on entry
static int trace_rw_entry(struct pt_regs *ctx, struct file *file,
char __user *buf, size_t count)
u32 tgid = bpf_get_current_pid_tgid() >> 32;
return 0;
u32 pid = bpf_get_current_pid_tgid();
// skip I/O lacking a filename
struct dentry *de = file->f_path.dentry;
int mode = file->f_inode->i_mode;
if (de->d_name.len == 0 || TYPE_FILTER)
return 0;
// store size and timestamp by pid
struct val_t val = {}; = count;
val.ts = bpf_ktime_get_ns();
struct qstr d_name = de->d_name;
val.name_len = d_name.len;
bpf_probe_read(&, sizeof(,;
bpf_get_current_comm(&val.comm, sizeof(val.comm));
entryinfo.update(&pid, &val);
return 0;
int trace_read_entry(struct pt_regs *ctx, struct file *file,
char __user *buf, size_t count)
// skip non-sync I/O; see kernel code for __vfs_read()
if (!(file->f_op->read_iter))
return 0;
return trace_rw_entry(ctx, file, buf, count);
int trace_write_entry(struct pt_regs *ctx, struct file *file,
char __user *buf, size_t count)
// skip non-sync I/O; see kernel code for __vfs_write()
if (!(file->f_op->write_iter))
return 0;
return trace_rw_entry(ctx, file, buf, count);
// output
static int trace_rw_return(struct pt_regs *ctx, int type)
struct val_t *valp;
u32 pid = bpf_get_current_pid_tgid();
valp = entryinfo.lookup(&pid);
if (valp == 0) {
// missed tracing issue or filtered
return 0;
u64 delta_us = (bpf_ktime_get_ns() - valp->ts) / 1000;
if (delta_us < MIN_US)
return 0;
struct data_t data = {};
data.mode = type; = pid; = valp->sz;
data.delta_us = delta_us;
data.name_len = valp->name_len;
bpf_probe_read(&, sizeof(, valp->name);
bpf_probe_read(&data.comm, sizeof(data.comm), valp->comm);
events.perf_submit(ctx, &data, sizeof(data));
return 0;
int trace_read_return(struct pt_regs *ctx)
return trace_rw_return(ctx, MODE_READ);
int trace_write_return(struct pt_regs *ctx)
return trace_rw_return(ctx, MODE_WRITE);
bpf_text = bpf_text.replace('MIN_US', str(min_ms * 1000))
if args.tgid:
bpf_text = bpf_text.replace('TGID_FILTER', 'tgid != %d' % tgid)
bpf_text = bpf_text.replace('TGID_FILTER', '0')
if args.all_files:
bpf_text = bpf_text.replace('TYPE_FILTER', '0')
bpf_text = bpf_text.replace('TYPE_FILTER', '!S_ISREG(mode)')
if debug or args.ebpf:
if args.ebpf:
# initialize BPF
b = BPF(text=bpf_text)
# I'd rather trace these via new_sync_read/new_sync_write (which used to be
# do_sync_read/do_sync_write), but those became static. So trace these from
# the parent functions, at the cost of more overhead, instead.
# Ultimately, we should be using [V]FS tracepoints.
b.attach_kprobe(event="__vfs_read", fn_name="trace_read_entry")
b.attach_kretprobe(event="__vfs_read", fn_name="trace_read_return")
b.attach_kprobe(event="__vfs_write", fn_name="trace_write_entry")
b.attach_kretprobe(event="__vfs_write", fn_name="trace_write_return")
except Exception:
# older kernels don't have __vfs_write so try vfs_write instead
b.attach_kprobe(event="vfs_write", fn_name="trace_write_entry")
b.attach_kretprobe(event="vfs_write", fn_name="trace_write_return")
mode_s = {
0: 'R',
1: 'W',
# header
print("Tracing sync read/writes slower than %d ms" % min_ms)
print("%-8s %-14s %-6s %1s %-7s %7s %s" % ("TIME(s)", "COMM", "TID", "D",
"BYTES", "LAT(ms)", "FILENAME"))
start_ts = time.time()
def print_event(cpu, data, size):
event = b["events"].event(data)
ms = float(event.delta_us) / 1000
name ='utf-8', 'replace')
if event.name_len > DNAME_INLINE_LEN:
name = name[:-3] + "..."
print("%-8.3f %-14.14s %-6s %1s %-7s %7.2f %s" % (
time.time() - start_ts, event.comm.decode('utf-8', 'replace'),, mode_s[event.mode],, ms, name))
b["events"].open_perf_buffer(print_event, page_cnt=64)
while 1:
except KeyboardInterrupt:
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