nfsdist tool (iovisor#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

@@ -0,0 +1,80 @@
+.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 @@ def test_nfsslower(self):
  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

@@ -0,0 +1,169 @@
+#!/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()