biolatency.py

#!/usr/bin/python
# @lint-avoid-python-3-compatibility-imports
#
# biolatency    Summarize block device I/O latency as a histogram.
#       For Linux, uses BCC, eBPF.
#
# USAGE: biolatency [-h] [-T] [-Q] [-m] [-D] [-e] [interval] [count]
#
# Copyright (c) 2015 Brendan Gregg.
# Licensed under the Apache License, Version 2.0 (the "License")
#
# 20-Sep-2015   Brendan Gregg   Created this.

from __future__ import print_function
from bcc import BPF
from time import sleep, strftime
import argparse
import ctypes as ct

# arguments
examples = """examples:
    ./biolatency                    # summarize block I/O latency as a histogram
    ./biolatency 1 10               # print 1 second summaries, 10 times
    ./biolatency -mT 1              # 1s summaries, milliseconds, and timestamps
    ./biolatency -Q                 # include OS queued time in I/O time
    ./biolatency -D                 # show each disk device separately
    ./biolatency -F                 # show I/O flags separately
    ./biolatency -j                 # print a dictionary
    ./biolatency -e                 # show extension summary(total, average)
"""
parser = argparse.ArgumentParser(
    description="Summarize block device I/O latency as a histogram",
    formatter_class=argparse.RawDescriptionHelpFormatter,
    epilog=examples)
parser.add_argument("-T", "--timestamp", action="store_true",
    help="include timestamp on output")
parser.add_argument("-Q", "--queued", action="store_true",
    help="include OS queued time in I/O time")
parser.add_argument("-m", "--milliseconds", action="store_true",
    help="millisecond histogram")
parser.add_argument("-D", "--disks", action="store_true",
    help="print a histogram per disk device")
parser.add_argument("-F", "--flags", action="store_true",
    help="print a histogram per set of I/O flags")
parser.add_argument("-e", "--extension", action="store_true",
    help="summarize average/total value")
parser.add_argument("interval", nargs="?", default=99999999,
    help="output interval, in seconds")
parser.add_argument("count", nargs="?", default=99999999,
    help="number of outputs")
parser.add_argument("--ebpf", action="store_true",
    help=argparse.SUPPRESS)
parser.add_argument("-j", "--json", action="store_true",
    help="json output")

args = parser.parse_args()
countdown = int(args.count)
debug = 0

if args.flags and args.disks:
    print("ERROR: can only use -D or -F. Exiting.")
    exit()

# define BPF program
bpf_text = """
#include <uapi/linux/ptrace.h>
#include <linux/blk-mq.h>

typedef struct disk_key {
    char disk[DISK_NAME_LEN];
    u64 slot;
} disk_key_t;

typedef struct flag_key {
    u64 flags;
    u64 slot;
} flag_key_t;

typedef struct ext_val {
    u64 total;
    u64 count;
} ext_val_t;

BPF_HASH(start, struct request *);
STORAGE

// time block I/O
int trace_req_start(struct pt_regs *ctx, struct request *req)
{
    u64 ts = bpf_ktime_get_ns();
    start.update(&req, &ts);
    return 0;
}

// output
int trace_req_done(struct pt_regs *ctx, struct request *req)
{
    u64 *tsp, delta;

    // fetch timestamp and calculate delta
    tsp = start.lookup(&req);
    if (tsp == 0) {
        return 0;   // missed issue
    }
    delta = bpf_ktime_get_ns() - *tsp;

    EXTENSION

    FACTOR

    // store as histogram
    STORE

    start.delete(&req);
    return 0;
}
"""

# code substitutions
if args.milliseconds:
    bpf_text = bpf_text.replace('FACTOR', 'delta /= 1000000;')
    label = "msecs"
else:
    bpf_text = bpf_text.replace('FACTOR', 'delta /= 1000;')
    label = "usecs"

storage_str = ""
store_str = ""
if args.disks:
    storage_str += "BPF_HISTOGRAM(dist, disk_key_t);"
    disks_str = """
    disk_key_t key = {.slot = bpf_log2l(delta)};
    void *__tmp = (void *)req->__RQ_DISK__->disk_name;
    bpf_probe_read(&key.disk, sizeof(key.disk), __tmp);
    dist.atomic_increment(key);
    """
    if BPF.kernel_struct_has_field(b'request', b'rq_disk'):
        store_str += disks_str.replace('__RQ_DISK__', 'rq_disk')
    else:
        store_str += disks_str.replace('__RQ_DISK__', 'q->disk')
elif args.flags:
    storage_str += "BPF_HISTOGRAM(dist, flag_key_t);"
    store_str += """
    flag_key_t key = {.slot = bpf_log2l(delta)};
    key.flags = req->cmd_flags;
    dist.atomic_increment(key);
    """
else:
    storage_str += "BPF_HISTOGRAM(dist);"
    store_str += "dist.atomic_increment(bpf_log2l(delta));"

if args.extension:
    storage_str += "BPF_ARRAY(extension, ext_val_t, 1);"
    bpf_text = bpf_text.replace('EXTENSION', """
    u32 index = 0;
    ext_val_t *ext_val = extension.lookup(&index);
    if (ext_val) {
        lock_xadd(&ext_val->total, delta);
        lock_xadd(&ext_val->count, 1);
    }
    """)
else:
    bpf_text = bpf_text.replace('EXTENSION', '')
bpf_text = bpf_text.replace("STORAGE", storage_str)
bpf_text = bpf_text.replace("STORE", store_str)

if debug or args.ebpf:
    print(bpf_text)
    if args.ebpf:
        exit()

# load BPF program
b = BPF(text=bpf_text)
if args.queued:
    if BPF.get_kprobe_functions(b'__blk_account_io_start'):
        b.attach_kprobe(event="__blk_account_io_start", fn_name="trace_req_start")
    else:
        b.attach_kprobe(event="blk_account_io_start", fn_name="trace_req_start")
else:
    if BPF.get_kprobe_functions(b'blk_start_request'):
        b.attach_kprobe(event="blk_start_request", fn_name="trace_req_start")
    b.attach_kprobe(event="blk_mq_start_request", fn_name="trace_req_start")
if BPF.get_kprobe_functions(b'__blk_account_io_done'):
    b.attach_kprobe(event="__blk_account_io_done", fn_name="trace_req_done")
else:
    b.attach_kprobe(event="blk_account_io_done", fn_name="trace_req_done")

if not args.json:
    print("Tracing block device I/O... Hit Ctrl-C to end.")

# see blk_fill_rwbs():
req_opf = {
    0: "Read",
    1: "Write",
    2: "Flush",
    3: "Discard",
    5: "SecureErase",
    6: "ZoneReset",
    7: "WriteSame",
    9: "WriteZeros"
}
REQ_OP_BITS = 8
REQ_OP_MASK = ((1 << REQ_OP_BITS) - 1)
REQ_SYNC = 1 << (REQ_OP_BITS + 3)
REQ_META = 1 << (REQ_OP_BITS + 4)
REQ_PRIO = 1 << (REQ_OP_BITS + 5)
REQ_NOMERGE = 1 << (REQ_OP_BITS + 6)
REQ_IDLE = 1 << (REQ_OP_BITS + 7)
REQ_FUA = 1 << (REQ_OP_BITS + 9)
REQ_RAHEAD = 1 << (REQ_OP_BITS + 11)
REQ_BACKGROUND = 1 << (REQ_OP_BITS + 12)
REQ_NOWAIT = 1 << (REQ_OP_BITS + 13)
def flags_print(flags):
    desc = ""
    # operation
    if flags & REQ_OP_MASK in req_opf:
        desc = req_opf[flags & REQ_OP_MASK]
    else:
        desc = "Unknown"
    # flags
    if flags & REQ_SYNC:
        desc = "Sync-" + desc
    if flags & REQ_META:
        desc = "Metadata-" + desc
    if flags & REQ_FUA:
        desc = "ForcedUnitAccess-" + desc
    if flags & REQ_PRIO:
        desc = "Priority-" + desc
    if flags & REQ_NOMERGE:
        desc = "NoMerge-" + desc
    if flags & REQ_IDLE:
        desc = "Idle-" + desc
    if flags & REQ_RAHEAD:
        desc = "ReadAhead-" + desc
    if flags & REQ_BACKGROUND:
        desc = "Background-" + desc
    if flags & REQ_NOWAIT:
        desc = "NoWait-" + desc
    return desc

# output
exiting = 0 if args.interval else 1
dist = b.get_table("dist")
if args.extension:
    extension = b.get_table("extension")
while (1):
    try:
        sleep(int(args.interval))
    except KeyboardInterrupt:
        exiting = 1

    print()
    if args.json:
        if args.timestamp:
            print("%-8s\n" % strftime("%H:%M:%S"), end="")

        if args.flags:
            dist.print_json_hist(label, "flags", flags_print)

        else:
            dist.print_json_hist(label)

    else:
        if args.timestamp:
            print("%-8s\n" % strftime("%H:%M:%S"), end="")

        if args.flags:
            dist.print_log2_hist(label, "flags", flags_print)
        else:
            dist.print_log2_hist(label, "disk")
        if args.extension:
            total = extension[0].total
            counts = extension[0].count
            if counts > 0:
                if label == 'msecs':
                    total /= 1000000
                elif label == 'usecs':
                    total /= 1000
                avg = total / counts
                print("\navg = %ld %s, total: %ld %s, count: %ld\n" %
                      (total / counts, label, total, label, counts))
            extension.clear()

    dist.clear()

    countdown -= 1
    if exiting or countdown == 0:
        exit()