xfsdist

README.md

@@ -99,7 +99,8 @@ Tools:
 - tools/[vfscount](tools/vfscount.py) tools/[vfscount.c](tools/vfscount.c): Count VFS calls. [Examples](tools/vfscount_example.txt).
 - tools/[vfsstat](tools/vfsstat.py) tools/[vfsstat.c](tools/vfsstat.c): Count some VFS calls, with column output. [Examples](tools/vfsstat_example.txt).
 - tools/[wakeuptime](tools/wakeuptime.py): Summarize sleep to wakeup time by waker kernel stack. [Examples](tools/wakeuptime_example.txt).
-- tools/[xfsslower](tools/xfsslower.py): Trace slow XFS operations: read, write, open, fsync. [Examples](tools/xfsslower_example.txt).
+- tools/[xfsdist](tools/xfsdist.py): Summarize XFS operation latency. [Examples](tools/xfsdist_example.txt).
+- tools/[xfsslower](tools/xfsslower.py): Trace slow XFS operations. [Examples](tools/xfsslower_example.txt).
 
 ### Networking
 

man/man8/xfsdist.8

+.TH xfsdist 8  "2016-02-12" "USER COMMANDS"
+.SH NAME
+xfsdist \- Summarize XFS operation latency. Uses Linux eBPF/bcc.
+.SH SYNOPSIS
+.B xfsdist [\-h] [\-T] [\-N] [\-d] [interval] [count]
+.SH DESCRIPTION
+This tool summarizes time (latency) spent in common XFS 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 xfs_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 XFS operation time, and print a summary on Ctrl-C:
+#
+.B xfsdist
+.TP
+Trace PID 181 only:
+#
+.B xfsdist -p 181
+.TP
+Print 1 second summaries, 10 times:
+#
+.B xfsdist 1 10
+.TP
+1 second summaries, printed in milliseconds
+#
+.B xfsdist \-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 these XFS operations,
+including reads and writes from the file system cache. 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
+xfssnoop(8)

tools/xfsdist.py

+#!/usr/bin/python
+# @lint-avoid-python-3-compatibility-imports
+#
+# xfsdist  Summarize XFS operation latency.
+#          For Linux, uses BCC, eBPF.
+#
+# USAGE: xfsdist [-h] [-T] [-m] [-p PID] [interval] [count]
+#
+# Copyright 2016 Netflix, Inc.
+# Licensed under the Apache License, Version 2.0 (the "License")
+#
+# 12-Feb-2016   Brendan Gregg   Created this.
+
+from __future__ import print_function
+from bcc import BPF
+from time import sleep, strftime
+import argparse
+
+# arguments
+examples = """examples:
+    ./xfsdist            # show operation latency as a histogram
+    ./xfsdist -p 181     # trace PID 181 only
+    ./xfsdist 1 10       # print 1 second summaries, 10 times
+    ./xfsdist -m 5       # 5s summaries, milliseconds
+"""
+parser = argparse.ArgumentParser(
+    description="Summarize XFS 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;
+}
+
+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);
+}
+"""
+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
+b.attach_kprobe(event="xfs_file_read_iter", fn_name="trace_entry")
+b.attach_kprobe(event="xfs_file_write_iter", fn_name="trace_entry")
+b.attach_kprobe(event="xfs_file_open", fn_name="trace_entry")
+b.attach_kprobe(event="xfs_file_fsync", fn_name="trace_entry")
+b.attach_kretprobe(event="xfs_file_read_iter", fn_name="trace_read_return")
+b.attach_kretprobe(event="xfs_file_write_iter", fn_name="trace_write_return")
+b.attach_kretprobe(event="xfs_file_open", fn_name="trace_open_return")
+b.attach_kretprobe(event="xfs_file_fsync", fn_name="trace_fsync_return")
+
+print("Tracing XFS 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()

tools/xfsdist_example.txt

+Demonstrations of xfsdist, the Linux eBPF/bcc version.
+
+
+xfsdist traces XFS reads, writes, opens, and fsyncs, and summarizes their
+latency as a power-of-2 histogram. For example:
+
+# ./xfsdist 
+Tracing XFS operation latency... Hit Ctrl-C to end.
+^C
+
+operation = 'read'
+     usecs               : count     distribution
+         0 -> 1          : 0        |                                        |
+         2 -> 3          : 362      |                                        |
+         4 -> 7          : 807      |*                                       |
+         8 -> 15         : 20686    |****************************************|
+        16 -> 31         : 512      |                                        |
+        32 -> 63         : 4        |                                        |
+        64 -> 127        : 2744     |*****                                   |
+       128 -> 255        : 7127     |*************                           |
+       256 -> 511        : 2483     |****                                    |
+       512 -> 1023       : 1281     |**                                      |
+      1024 -> 2047       : 39       |                                        |
+      2048 -> 4095       : 5        |                                        |
+      4096 -> 8191       : 1        |                                        |
+
+operation = 'open'
+     usecs               : count     distribution
+         0 -> 1          : 0        |                                        |
+         2 -> 3          : 3        |****************************************|
+
+This output shows a bi-modal distribution for read latency, with a faster
+mode of 20,686 reads that took between 8 and 15 microseconds, and a slower
+mode of over 10,000 reads that took between 64 and 1023 microseconds. It's
+likely that the faster mode was a hit from the in-memory file system cache,
+and the slower mode is a read from a storage device (disk).
+
+This "latency" is measured from when the operation was issued from the VFS
+interface to the file system, to when it completed. This spans everything:
+block device I/O (disk I/O), file system CPU cycles, file system locks, run
+queue latency, etc. This is a better measure of the latency suffered by
+applications reading from the file system than measuring this down at the
+block device interface.
+
+Note that this only traces the common file system operations previously
+listed: other file system operations (eg, inode operations including
+getattr()) are not traced.
+
+
+An optional interval and a count can be provided, as well as -m to show the
+distributions in milliseconds. For example:
+
+# ./xfsdist -m 1 5
+Tracing XFS operation latency... Hit Ctrl-C to end.
+
+10:14:15:
+
+operation = 'read'
+     msecs               : count     distribution
+         0 -> 1          : 1366     |****************************************|
+         2 -> 3          : 86       |**                                      |
+         4 -> 7          : 95       |**                                      |
+         8 -> 15         : 132      |***                                     |
+        16 -> 31         : 72       |**                                      |
+
+operation = 'write'
+     msecs               : count     distribution
+         0 -> 1          : 685      |****************************************|
+
+10:14:16:
+
+operation = 'read'
+     msecs               : count     distribution
+         0 -> 1          : 984      |****************************************|
+         2 -> 3          : 66       |**                                      |
+         4 -> 7          : 67       |**                                      |
+         8 -> 15         : 104      |****                                    |
+        16 -> 31         : 70       |**                                      |
+        32 -> 63         : 12       |                                        |
+
+operation = 'write'
+     msecs               : count     distribution
+         0 -> 1          : 536      |****************************************|
+
+10:14:17:
+
+operation = 'read'
+     msecs               : count     distribution
+         0 -> 1          : 1262     |****************************************|
+         2 -> 3          : 75       |**                                      |
+         4 -> 7          : 80       |**                                      |
+         8 -> 15         : 119      |***                                     |
+        16 -> 31         : 75       |**                                      |
+        32 -> 63         : 3        |                                        |
+
+operation = 'write'
+     msecs               : count     distribution
+         0 -> 1          : 639      |****************************************|
+
+10:14:18:
+
+operation = 'read'
+     msecs               : count     distribution
+         0 -> 1          : 1070     |****************************************|
+         2 -> 3          : 58       |**                                      |
+         4 -> 7          : 74       |**                                      |
+         8 -> 15         : 140      |*****                                   |
+        16 -> 31         : 60       |**                                      |
+        32 -> 63         : 5        |                                        |
+
+operation = 'write'
+     msecs               : count     distribution
+         0 -> 1          : 556      |****************************************|
+
+10:14:19:
+
+operation = 'read'
+     msecs               : count     distribution
+         0 -> 1          : 1176     |****************************************|
+         2 -> 3          : 53       |*                                       |
+         4 -> 7          : 94       |***                                     |
+         8 -> 15         : 112      |***                                     |
+        16 -> 31         : 77       |**                                      |
+        32 -> 63         : 3        |                                        |
+
+operation = 'write'
+     msecs               : count     distribution
+         0 -> 1          : 613      |****************************************|
+
+This shows a mixed read/write workload, where the slower read mode was around
+10 ms.
+
+
+USAGE message:
+
+# ./xfsdist -h
+usage: xfsdist [-h] [-T] [-m] [-p PID] [interval] [count]
+
+Summarize XFS operation latency
+
+positional arguments:
+  interval            output interval, in seconds
+  count               number of outputs
+
+optional arguments:
+  -h, --help          show this help message and exit
+  -T, --notimestamp   don't include timestamp on interval output
+  -m, --milliseconds  output in milliseconds
+  -p PID, --pid PID   trace this PID only
+
+examples:
+    ./xfsdist            # show operation latency as a histogram
+    ./xfsdist -p 181     # trace PID 181 only
+    ./xfsdist 1 10       # print 1 second summaries, 10 times
+    ./xfsdist -m 5       # 5s summaries, milliseconds