nfsdist tool (#1347)

nfsdist: trace NFS operation latency distribution, similar to the other *dist tools.

README.md

@@ -118,6 +118,7 @@ pair of .c and .py files, and some are directories of files.
 - tools/[mysqld_qslower](tools/mysqld_qslower.py): Trace MySQL server queries slower than a threshold. [Examples](tools/mysqld_qslower_example.txt).
 - tools/[memleak](tools/memleak.py): Display outstanding memory allocations to find memory leaks. [Examples](tools/memleak_example.txt).
 - tools/[nfsslower](tools/nfsslower.py): Trace slow NFS operations. [Examples](tools/nfsslower_example.txt).
+- tools/[nfsdist](tools/nfsdist.py): Summarize NFS operation latency distribution as a histogram. [Examples](tools/nfsdist_example.txt).
 - tools/[offcputime](tools/offcputime.py): Summarize off-CPU time by kernel stack trace. [Examples](tools/offcputime_example.txt).
 - tools/[offwaketime](tools/offwaketime.py): Summarize blocked time by kernel off-CPU stack and waker stack. [Examples](tools/offwaketime_example.txt).
 - tools/[oomkill](tools/oomkill.py): Trace the out-of-memory (OOM) killer. [Examples](tools/oomkill_example.txt).

man/man8/nfsdist.8

+.TH nfsdist 8  "2017-09-08" "USER COMMANDS"
+.SH NAME
+nfsdist \- Summarize NFS operation latency. Uses Linux eBPF/bcc.
+.SH SYNOPSIS
+.B nfsdist [\-h] [\-T] [\-m] [\-p PID] [interval] [count]
+.SH DESCRIPTION
+This tool summarizes time (latency) spent in common NFS file operations: reads,
+writes, opens, and getattrs, 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 nfs_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 NFS operation time, and print a summary on Ctrl-C:
+#
+.B nfsdist
+.TP
+Trace PID 181 only:
+#
+.B nfsdist -p 181
+.TP
+Print 1 second summaries, 10 times:
+#
+.B nfsdist 1 10
+.TP
+1 second summaries, printed in milliseconds
+#
+.B nfsdist \-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 NFS 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
+Samuel Nair
+.SH SEE ALSO
+nfsslower(8)

tests/python/test_tools_smoke.py

@@ -225,6 +225,13 @@ class SmokeTests(TestCase):
         else:
             pass
 
+    @skipUnless(kernel_version_ge(4,4), "requires kernel >= 4.4")
+    def test_nfsdist(self):
+        if(self.kmod_loaded("nfs")):
+            self.run_with_duration("nfsdist.py 1 1")
+        else:
+            pass
+
     @skipUnless(kernel_version_ge(4,6), "requires kernel >= 4.6")
     def test_offcputime(self):
         self.run_with_duration("offcputime.py 1")

tools/nfsdist.py

+#!/usr/bin/python
+# @lint-avoid-python-3-compatibility-imports
+#
+# nfsdist   Summarize NFS operation latency
+#           for Linux, uses BCC and eBPF
+#
+# USAGE: nfsdist [-h] [-T] [-m] [-p PID] [interval] [count]
+#
+# 4-Sep-2017    Samuel Nair     created this
+
+from __future__ import print_function
+from bcc import BPF
+from time import sleep, strftime
+import argparse
+
+# arguments
+examples = """examples:
+    ./nfsdist            # show operation latency as a histogram
+    ./nfsdist -p 181     # trace PID 181 only
+    ./nfsdist 1 10       # print 1 second summaries, 10 times
+    ./nfsdist -m 5       # 5s summaries, milliseconds
+"""
+parser = argparse.ArgumentParser(
+        description="Summarize NFS 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_getattr_return(struct pt_regs *ctx)
+{
+    char *op = "getattr";
+    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="nfs_file_read", fn_name="trace_entry")
+b.attach_kprobe(event="nfs_file_write", fn_name="trace_entry")
+b.attach_kprobe(event="nfs4_file_open", fn_name="trace_entry")
+b.attach_kprobe(event="nfs_file_open", fn_name="trace_entry")
+b.attach_kprobe(event="nfs_getattr", fn_name="trace_entry")
+
+b.attach_kretprobe(event="nfs_file_read", fn_name="trace_read_return")
+b.attach_kretprobe(event="nfs_file_write", fn_name="trace_write_return")
+b.attach_kretprobe(event="nfs4_file_open", fn_name="trace_open_return")
+b.attach_kretprobe(event="nfs_file_open", fn_name="trace_open_return")
+b.attach_kretprobe(event="nfs_getattr", fn_name="trace_getattr_return")
+
+print("Tracing NFS 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", section_print_fn=bytes.decode)
+    dist.clear()
+
+    countdown -= 1
+    if exiting or countdown == 0:
+        exit()

tools/nfsdist_example.txt

+Demonstrations of nfsdist, the Linux eBPF/bcc version.
+
+nfsdist traces NFS reads, writes, opens, and getattr, and summarizes their
+latency as a power-of-2 histogram. For example:
+
+
+./nfsdist.py
+
+Tracing NFS operation latency... Hit Ctrl-C to end.
+
+operation = read
+     usecs               : count     distribution
+         0 -> 1          : 4        |                                        |
+         2 -> 3          : 0        |                                        |
+         4 -> 7          : 0        |                                        |
+         8 -> 15         : 7107     |**************                          |
+        16 -> 31         : 19864    |****************************************|
+        32 -> 63         : 1494     |***                                     |
+        64 -> 127        : 491      |                                        |
+       128 -> 255        : 1810     |***                                     |
+       256 -> 511        : 6356     |************                            |
+       512 -> 1023       : 4860     |*********                               |
+      1024 -> 2047       : 3070     |******                                  |
+      2048 -> 4095       : 1853     |***                                     |
+      4096 -> 8191       : 921      |*                                       |
+      8192 -> 16383      : 122      |                                        |
+     16384 -> 32767      : 15       |                                        |
+     32768 -> 65535      : 5        |                                        |
+     65536 -> 131071     : 2        |                                        |
+    131072 -> 262143     : 1        |                                        |
+
+operation = write
+     usecs               : count     distribution
+         0 -> 1          : 0        |                                        |
+         2 -> 3          : 0        |                                        |
+         4 -> 7          : 0        |                                        |
+         8 -> 15         : 1        |                                        |
+        16 -> 31         : 0        |                                        |
+        32 -> 63         : 9        |                                        |
+        64 -> 127        : 19491    |****************************************|
+       128 -> 255        : 3064     |******                                  |
+       256 -> 511        : 940      |*                                       |
+       512 -> 1023       : 365      |                                        |
+      1024 -> 2047       : 312      |                                        |
+      2048 -> 4095       : 119      |                                        |
+      4096 -> 8191       : 31       |                                        |
+      8192 -> 16383      : 84       |                                        |
+     16384 -> 32767      : 31       |                                        |
+     32768 -> 65535      : 5        |                                        |
+     65536 -> 131071     : 3        |                                        |
+    131072 -> 262143     : 0        |                                        |
+    262144 -> 524287     : 1        |                                        |
+
+operation = getattr
+     usecs               : count     distribution
+         0 -> 1          : 27       |****************************************|
+         2 -> 3          : 2        |**                                      |
+         4 -> 7          : 3        |****                                    |
+         8 -> 15         : 0        |                                        |
+        16 -> 31         : 0        |                                        |
+        32 -> 63         : 0        |                                        |
+        64 -> 127        : 0        |                                        |
+       128 -> 255        : 0        |                                        |
+       256 -> 511        : 2        |**                                      |
+       512 -> 1023       : 2        |**                                      |
+
+operation = open
+     usecs               : count     distribution
+         0 -> 1          : 0        |                                        |
+         2 -> 3          : 0        |                                        |
+         4 -> 7          : 0        |                                        |
+         8 -> 15         : 0        |                                        |
+        16 -> 31         : 0        |                                        |
+        32 -> 63         : 0        |                                        |
+        64 -> 127        : 0        |                                        |
+       128 -> 255        : 0        |                                        |
+       256 -> 511        : 2        |****************************************|
+
+
+In this example you can see that the read traffic is rather bi-modal, with about
+26K reads falling within 8 - 30 usecs and about 18K reads spread between 128 -
+8191 usecs. Write traffic is largely clustered in the 64 - 127 usecs bracket.
+The faster read traffic is probably coming from a filesystem cache and the slower
+traffic from disk. The reason why the writes are so consistently fast is because
+this example test was run on a couple of VM's and I believe the hypervisor was
+caching all the write traffic to memory.
+
+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:
+RPC latency, network latency, file system CPU cycles, file system locks, run
+queue latency, etc. This is a better measure of the latency suffered by
+applications reading from a NFS share and can better expose problems
+experienced by NFS clients.
+
+Note that this only traces the common NFS operations (read, write, open and
+getattr). I chose to include getattr as a significant percentage of NFS
+traffic end up being getattr calls and are a good indicator of problems
+with an NFS server.
+
+An optional interval and a count can be provided, as well as -m to show the
+distributions in milliseconds. For example:
+
+./nfsdist -m 1 5
+Tracing NFS operation latency... Hit Ctrl-C to end.
+
+11:02:39:
+
+operation = write
+     msecs               : count     distribution
+         0 -> 1          : 1        |                                        |
+         2 -> 3          : 24       |********                                |
+         4 -> 7          : 114      |****************************************|
+         8 -> 15         : 9        |***                                     |
+        16 -> 31         : 1        |                                        |
+        32 -> 63         : 1        |                                        |
+
+11:02:40:
+
+operation = write
+     msecs               : count     distribution
+         0 -> 1          : 0        |                                        |
+         2 -> 3          : 11       |***                                     |
+         4 -> 7          : 111      |****************************************|
+         8 -> 15         : 13       |****                                    |
+        16 -> 31         : 1        |                                        |
+
+11:02:41:
+
+operation = write
+     msecs               : count     distribution
+         0 -> 1          : 0        |                                        |
+         2 -> 3          : 21       |******                                  |
+         4 -> 7          : 137      |****************************************|
+         8 -> 15         : 3        |                                        |
+
+This shows a write workload, with writes hovering primarily in the 4-7ms range.
+
+USAGE message:
+
+
+./nfsdist -h
+usage: nfsdist.py [-h] [-T] [-m] [-p PID] [interval] [count]
+
+Summarize NFS 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:
+    ./nfsdist            # show operation latency as a histogram
+    ./nfsdist -p 181     # trace PID 181 only
+    ./nfsdist 1 10       # print 1 second summaries, 10 times
+    ./nfsdist -m 5       # 5s summaries, milliseconds