btrfsdist

README.md

@@ -71,6 +71,7 @@ Tools:
 - tools/[biotop](tools/biotop.py): Top for disks: Summarize block device I/O by process. [Examples](tools/biotop_example.txt).
 - tools/[biosnoop](tools/biosnoop.py): Trace block device I/O with PID and latency. [Examples](tools/biosnoop_example.txt).
 - tools/[bitesize](tools/bitesize.py): Show per process I/O size histogram. [Examples](tools/bitesize_example.txt).
+- tools/[btrfsdist](tools/btrfsdist.py): Summarize btrfs operation latency distribution as a histogram. [Examples](tools/btrfsdist_example.txt).
 - tools/[btrfsslower](tools/btrfsslower.py): Trace slow btrfs operations. [Examples](tools/btrfsslower_example.txt).
 - tools/[cachestat](tools/cachestat.py): Trace page cache hit/miss ratio. [Examples](tools/cachestat_example.txt).
 - tools/[dcsnoop](tools/dcsnoop.py): Trace directory entry cache (dcache) lookups. [Examples](tools/dcsnoop_example.txt).

man/man8/btrfsdist.8

@@ -0,0 +1,82 @@
+.TH btrfsdist 8 "2016-02-15" "USER COMMANDS"
+.SH NAME
+btrfsdist \- Summarize btrfs operation latency. Uses Linux eBPF/bcc.
+.SH SYNOPSIS
+.B btrfsdist [\-h] [\-T] [\-N] [\-d] [interval] [count]
+.SH DESCRIPTION
+This tool summarizes time (latency) spent in common btrfs file operations:
+reads, writes, opens, and syncs, and presents it as a power-of-2 histogram. It
+uses an in-kernel eBPF map to store the histogram for efficiency.
+
+Since this works by tracing the btrfs_file_operations interface functions, it
+will need updating to match any changes to these functions.
+
+Since this uses BPF, only the root user can use this tool.
+.SH REQUIREMENTS
+CONFIG_BPF and bcc.
+.SH OPTIONS
+.TP
+\-h
+Print usage message.
+.TP
+\-T
+Don't include timestamps on interval output.
+.TP
+\-m
+Output in milliseconds.
+.TP
+\-p PID
+Trace this PID only.
+.SH EXAMPLES
+.TP
+Trace btrfs operation time, and print a summary on Ctrl-C:
+#
+.B btrfsdist
+.TP
+Trace PID 181 only:
+#
+.B btrfsdist -p 181
+.TP
+Print 1 second summaries, 10 times:
+#
+.B btrfsdist 1 10
+.TP
+1 second summaries, printed in milliseconds
+#
+.B btrfsdist \-m 1
+.SH FIELDS
+.TP
+msecs
+Range of milliseconds for this bucket.
+.TP
+usecs
+Range of microseconds for this bucket.
+.TP
+count
+Number of operations in this time range.
+.TP
+distribution
+ASCII representation of the distribution (the count column).
+.SH OVERHEAD
+This adds low-overhead instrumentation to btrfs writes and fsyncs, as well
+as all system reads and opens (due to the current implementation of the
+btrfs_file_operations interface). Particularly, all reads and writes from
+the file system cache will incur extra overhead while tracing. Such reads and
+writes can be very frequent (depending on the workload; eg, 1M/sec), at which
+point the overhead of this tool may become noticeable.
+Measure and quantify before use.
+.SH SOURCE
+This is from bcc.
+.IP
+https://github.com/iovisor/bcc
+.PP
+Also look in the bcc distribution for a companion _examples.txt file containing
+example usage, output, and commentary for this tool.
+.SH OS
+Linux
+.SH STABILITY
+Unstable - in development.
+.SH AUTHOR
+Brendan Gregg
+.SH SEE ALSO
+btrfsslower(8)

tools/btrfsdist.py

@@ -0,0 +1,223 @@
+#!/usr/bin/python
+# @lint-avoid-python-3-compatibility-imports
+#
+# btrfsdist Summarize btrfs operation latency.
+# For Linux, uses BCC, eBPF.
+#
+# USAGE: btrfsdist [-h] [-T] [-m] [-p PID] [interval] [count]
+#
+# Copyright 2016 Netflix, Inc.
+# Licensed under the Apache License, Version 2.0 (the "License")
+#
+# 15-Feb-2016 Brendan Gregg Created this.
+
+from __future__ import print_function
+from bcc import BPF
+from time import sleep, strftime
+import argparse
+
+# symbols
+kallsyms = "/proc/kallsyms"
+
+# arguments
+examples = """examples:
+ ./btrfsdist # show operation latency as a histogram
+ ./btrfsdist -p 181 # trace PID 181 only
+ ./btrfsdist 1 10 # print 1 second summaries, 10 times
+ ./btrfsdist -m 5 # 5s summaries, milliseconds
+"""
+parser = argparse.ArgumentParser(
+ description="Summarize btrfs operation latency",
+ formatter_class=argparse.RawDescriptionHelpFormatter,
+ epilog=examples)
+parser.add_argument("-T", "--notimestamp", action="store_true",
+ help="don't include timestamp on interval output")
+parser.add_argument("-m", "--milliseconds", action="store_true",
+ help="output in milliseconds")
+parser.add_argument("-p", "--pid",
+ help="trace this PID only")
+parser.add_argument("interval", nargs="?",
+ help="output interval, in seconds")
+parser.add_argument("count", nargs="?", default=99999999,
+ help="number of outputs")
+args = parser.parse_args()
+pid = args.pid
+countdown = int(args.count)
+if args.milliseconds:
+ factor = 1000000
+ label = "msecs"
+else:
+ factor = 1000
+ label = "usecs"
+if args.interval and int(args.interval) == 0:
+ print("ERROR: interval 0. Exiting.")
+ exit()
+debug = 0
+
+# define BPF program
+bpf_text = """
+#include <uapi/linux/ptrace.h>
+#include <linux/fs.h>
+#include <linux/sched.h>
+
+#define OP_NAME_LEN 8
+typedef struct dist_key {
+ char op[OP_NAME_LEN];
+ u64 slot;
+} dist_key_t;
+BPF_HASH(start, u32);
+BPF_HISTOGRAM(dist, dist_key_t);
+
+// time operation
+int trace_entry(struct pt_regs *ctx)
+{
+ u32 pid = bpf_get_current_pid_tgid();
+ if (FILTER_PID)
+ return 0;
+ u64 ts = bpf_ktime_get_ns();
+ start.update(&pid, &ts);
+ return 0;
+}
+
+// The current btrfs (Linux 4.5) uses generic_file_read_iter() instead of it's
+// own read function. So we need to trace that and then filter on btrfs, which
+// I do by checking file->f_op.
+int trace_read_entry(struct pt_regs *ctx, struct kiocb *iocb)
+{
+ u32 pid = bpf_get_current_pid_tgid();
+ if (FILTER_PID)
+ return 0;
+
+ // btrfs filter on file->f_op == btrfs_file_operations
+ struct file *fp = iocb->ki_filp;
+ if ((u64)fp->f_op != BTRFS_FILE_OPERATIONS)
+ return 0;
+
+ u64 ts = bpf_ktime_get_ns();
+ start.update(&pid, &ts);
+ return 0;
+}
+
+// The current btrfs (Linux 4.5) uses generic_file_open(), instead of it's own
+// function. Same as with reads. Trace the generic path and filter:
+int trace_open_entry(struct pt_regs *ctx, struct inode *inode,
+ struct file *file)
+{
+ u32 pid;
+ pid = bpf_get_current_pid_tgid();
+ if (FILTER_PID)
+ return 0;
+
+ // btrfs filter on file->f_op == btrfs_file_operations
+ if ((u64)file->f_op != BTRFS_FILE_OPERATIONS)
+ return 0;
+
+ u64 ts = bpf_ktime_get_ns();
+ start.update(&pid, &ts);
+ return 0;
+}
+
+static int trace_return(struct pt_regs *ctx, const char *op)
+{
+ u64 *tsp;
+ u32 pid = bpf_get_current_pid_tgid();
+
+ // fetch timestamp and calculate delta
+ tsp = start.lookup(&pid);
+ if (tsp == 0) {
+ return 0; // missed start or filtered
+ }
+ u64 delta = (bpf_ktime_get_ns() - *tsp) / FACTOR;
+
+ // store as histogram
+ dist_key_t key = {.slot = bpf_log2l(delta)};
+ __builtin_memcpy(&key.op, op, sizeof(key.op));
+ dist.increment(key);
+
+ start.delete(&pid);
+ return 0;
+}
+
+int trace_read_return(struct pt_regs *ctx)
+{
+ char *op = "read";
+ return trace_return(ctx, op);
+}
+
+int trace_write_return(struct pt_regs *ctx)
+{
+ char *op = "write";
+ return trace_return(ctx, op);
+}
+
+int trace_open_return(struct pt_regs *ctx)
+{
+ char *op = "open";
+ return trace_return(ctx, op);
+}
+
+int trace_fsync_return(struct pt_regs *ctx)
+{
+ char *op = "fsync";
+ return trace_return(ctx, op);
+}
+"""
+
+# code replacements
+with open(kallsyms) as syms:
+ ops = ''
+ for line in syms:
+ a = line.rstrip().split()
+ (addr, name) = (a[0], a[2])
+ if name == "btrfs_file_operations":
+ ops = "0x" + addr
+ break
+ if ops == '':
+ print("ERROR: no btrfs_file_operations in /proc/kallsyms. Exiting.")
+ exit()
+ bpf_text = bpf_text.replace('BTRFS_FILE_OPERATIONS', ops)
+bpf_text = bpf_text.replace('FACTOR', str(factor))
+if args.pid:
+ bpf_text = bpf_text.replace('FILTER_PID', 'pid != %s' % pid)
+else:
+ bpf_text = bpf_text.replace('FILTER_PID', '0')
+if debug:
+ print(bpf_text)
+
+# load BPF program
+b = BPF(text=bpf_text)
+
+# Common file functions. See earlier comment about generic_file_read_iter().
+b.attach_kprobe(event="generic_file_read_iter", fn_name="trace_read_entry")
+b.attach_kprobe(event="btrfs_file_write_iter", fn_name="trace_entry")
+b.attach_kprobe(event="generic_file_open", fn_name="trace_open_entry")
+b.attach_kprobe(event="btrfs_sync_file", fn_name="trace_entry")
+b.attach_kretprobe(event="generic_file_read_iter", fn_name="trace_read_return")
+b.attach_kretprobe(event="btrfs_file_write_iter", fn_name="trace_write_return")
+b.attach_kretprobe(event="generic_file_open", fn_name="trace_open_return")
+b.attach_kretprobe(event="btrfs_sync_file", fn_name="trace_fsync_return")
+
+print("Tracing btrfs operation latency... Hit Ctrl-C to end.")
+
+# output
+exiting = 0
+dist = b.get_table("dist")
+while (1):
+ try:
+ if args.interval:
+ sleep(int(args.interval))
+ else:
+ sleep(99999999)
+ except KeyboardInterrupt:
+ exiting = 1
+
+ print()
+ if args.interval and (not args.notimestamp):
+ print(strftime("%H:%M:%S:"))
+
+ dist.print_log2_hist(label, "operation")
+ dist.clear()
+
+ countdown -= 1
+ if exiting or countdown == 0:
+ exit()