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Documentation / filesystems / nfs / knfsd-stats.txt

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Based on kernel version 4.3. Page generated on 2015-11-02 12:49 EST.

2	Kernel NFS Server Statistics
3	============================
5	This document describes the format and semantics of the statistics
6	which the kernel NFS server makes available to userspace.  These
7	statistics are available in several text form pseudo files, each of
8	which is described separately below.
10	In most cases you don't need to know these formats, as the nfsstat(8)
11	program from the nfs-utils distribution provides a helpful command-line
12	interface for extracting and printing them.
14	All the files described here are formatted as a sequence of text lines,
15	separated by newline '\n' characters.  Lines beginning with a hash
16	'#' character are comments intended for humans and should be ignored
17	by parsing routines.  All other lines contain a sequence of fields
18	separated by whitespace.
20	/proc/fs/nfsd/pool_stats
21	------------------------
23	This file is available in kernels from 2.6.30 onwards, if the
24	/proc/fs/nfsd filesystem is mounted (it almost always should be).
26	The first line is a comment which describes the fields present in
27	all the other lines.  The other lines present the following data as
28	a sequence of unsigned decimal numeric fields.  One line is shown
29	for each NFS thread pool.
31	All counters are 64 bits wide and wrap naturally.  There is no way
32	to zero these counters, instead applications should do their own
33	rate conversion.
35	pool
36		The id number of the NFS thread pool to which this line applies.
37		This number does not change.
39		Thread pool ids are a contiguous set of small integers starting
40		at zero.  The maximum value depends on the thread pool mode, but
41		currently cannot be larger than the number of CPUs in the system.
42		Note that in the default case there will be a single thread pool
43		which contains all the nfsd threads and all the CPUs in the system,
44		and thus this file will have a single line with a pool id of "0".
46	packets-arrived
47		Counts how many NFS packets have arrived.  More precisely, this
48		is the number of times that the network stack has notified the
49		sunrpc server layer that new data may be available on a transport
50		(e.g. an NFS or UDP socket or an NFS/RDMA endpoint).
52		Depending on the NFS workload patterns and various network stack
53		effects (such as Large Receive Offload) which can combine packets
54		on the wire, this may be either more or less than the number
55		of NFS calls received (which statistic is available elsewhere).
56		However this is a more accurate and less workload-dependent measure
57		of how much CPU load is being placed on the sunrpc server layer
58		due to NFS network traffic.
60	sockets-enqueued
61		Counts how many times an NFS transport is enqueued to wait for
62		an nfsd thread to service it, i.e. no nfsd thread was considered
63		available.
65		The circumstance this statistic tracks indicates that there was NFS
66		network-facing work to be done but it couldn't be done immediately,
67		thus introducing a small delay in servicing NFS calls.  The ideal
68		rate of change for this counter is zero; significantly non-zero
69		values may indicate a performance limitation.
71		This can happen because there are too few nfsd threads in the thread
72		pool for the NFS workload (the workload is thread-limited), in which
73		case configuring more nfsd threads will probably improve the
74		performance of the NFS workload.
76	threads-woken
77		Counts how many times an idle nfsd thread is woken to try to
78		receive some data from an NFS transport.
80		This statistic tracks the circumstance where incoming
81		network-facing NFS work is being handled quickly, which is a good
82		thing.  The ideal rate of change for this counter will be close
83		to but less than the rate of change of the packets-arrived counter.
85	threads-timedout
86		Counts how many times an nfsd thread triggered an idle timeout,
87		i.e. was not woken to handle any incoming network packets for
88		some time.
90		This statistic counts a circumstance where there are more nfsd
91		threads configured than can be used by the NFS workload.  This is
92		a clue that the number of nfsd threads can be reduced without
93		affecting performance.  Unfortunately, it's only a clue and not
94		a strong indication, for a couple of reasons:
96		 - Currently the rate at which the counter is incremented is quite
97		   slow; the idle timeout is 60 minutes.  Unless the NFS workload
98		   remains constant for hours at a time, this counter is unlikely
99		   to be providing information that is still useful.
101		 - It is usually a wise policy to provide some slack,
102		   i.e. configure a few more nfsds than are currently needed,
103		   to allow for future spikes in load.
106	Note that incoming packets on NFS transports will be dealt with in
107	one of three ways.  An nfsd thread can be woken (threads-woken counts
108	this case), or the transport can be enqueued for later attention
109	(sockets-enqueued counts this case), or the packet can be temporarily
110	deferred because the transport is currently being used by an nfsd
111	thread.  This last case is not very interesting and is not explicitly
112	counted, but can be inferred from the other counters thus:
114	packets-deferred = packets-arrived - ( sockets-enqueued + threads-woken )
117	More
118	----
119	Descriptions of the other statistics file should go here.
122	Greg Banks <gnb@sgi.com>
123	26 Mar 2009
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