160 lines
6.6 KiB
Plaintext
160 lines
6.6 KiB
Plaintext
|
|
Kernel NFS Server Statistics
|
|
============================
|
|
|
|
This document describes the format and semantics of the statistics
|
|
which the kernel NFS server makes available to userspace. These
|
|
statistics are available in several text form pseudo files, each of
|
|
which is described separately below.
|
|
|
|
In most cases you don't need to know these formats, as the nfsstat(8)
|
|
program from the nfs-utils distribution provides a helpful command-line
|
|
interface for extracting and printing them.
|
|
|
|
All the files described here are formatted as a sequence of text lines,
|
|
separated by newline '\n' characters. Lines beginning with a hash
|
|
'#' character are comments intended for humans and should be ignored
|
|
by parsing routines. All other lines contain a sequence of fields
|
|
separated by whitespace.
|
|
|
|
/proc/fs/nfsd/pool_stats
|
|
------------------------
|
|
|
|
This file is available in kernels from 2.6.30 onwards, if the
|
|
/proc/fs/nfsd filesystem is mounted (it almost always should be).
|
|
|
|
The first line is a comment which describes the fields present in
|
|
all the other lines. The other lines present the following data as
|
|
a sequence of unsigned decimal numeric fields. One line is shown
|
|
for each NFS thread pool.
|
|
|
|
All counters are 64 bits wide and wrap naturally. There is no way
|
|
to zero these counters, instead applications should do their own
|
|
rate conversion.
|
|
|
|
pool
|
|
The id number of the NFS thread pool to which this line applies.
|
|
This number does not change.
|
|
|
|
Thread pool ids are a contiguous set of small integers starting
|
|
at zero. The maximum value depends on the thread pool mode, but
|
|
currently cannot be larger than the number of CPUs in the system.
|
|
Note that in the default case there will be a single thread pool
|
|
which contains all the nfsd threads and all the CPUs in the system,
|
|
and thus this file will have a single line with a pool id of "0".
|
|
|
|
packets-arrived
|
|
Counts how many NFS packets have arrived. More precisely, this
|
|
is the number of times that the network stack has notified the
|
|
sunrpc server layer that new data may be available on a transport
|
|
(e.g. an NFS or UDP socket or an NFS/RDMA endpoint).
|
|
|
|
Depending on the NFS workload patterns and various network stack
|
|
effects (such as Large Receive Offload) which can combine packets
|
|
on the wire, this may be either more or less than the number
|
|
of NFS calls received (which statistic is available elsewhere).
|
|
However this is a more accurate and less workload-dependent measure
|
|
of how much CPU load is being placed on the sunrpc server layer
|
|
due to NFS network traffic.
|
|
|
|
sockets-enqueued
|
|
Counts how many times an NFS transport is enqueued to wait for
|
|
an nfsd thread to service it, i.e. no nfsd thread was considered
|
|
available.
|
|
|
|
The circumstance this statistic tracks indicates that there was NFS
|
|
network-facing work to be done but it couldn't be done immediately,
|
|
thus introducing a small delay in servicing NFS calls. The ideal
|
|
rate of change for this counter is zero; significantly non-zero
|
|
values may indicate a performance limitation.
|
|
|
|
This can happen either because there are too few nfsd threads in the
|
|
thread pool for the NFS workload (the workload is thread-limited),
|
|
or because the NFS workload needs more CPU time than is available in
|
|
the thread pool (the workload is CPU-limited). In the former case,
|
|
configuring more nfsd threads will probably improve the performance
|
|
of the NFS workload. In the latter case, the sunrpc server layer is
|
|
already choosing not to wake idle nfsd threads because there are too
|
|
many nfsd threads which want to run but cannot, so configuring more
|
|
nfsd threads will make no difference whatsoever. The overloads-avoided
|
|
statistic (see below) can be used to distinguish these cases.
|
|
|
|
threads-woken
|
|
Counts how many times an idle nfsd thread is woken to try to
|
|
receive some data from an NFS transport.
|
|
|
|
This statistic tracks the circumstance where incoming
|
|
network-facing NFS work is being handled quickly, which is a good
|
|
thing. The ideal rate of change for this counter will be close
|
|
to but less than the rate of change of the packets-arrived counter.
|
|
|
|
overloads-avoided
|
|
Counts how many times the sunrpc server layer chose not to wake an
|
|
nfsd thread, despite the presence of idle nfsd threads, because
|
|
too many nfsd threads had been recently woken but could not get
|
|
enough CPU time to actually run.
|
|
|
|
This statistic counts a circumstance where the sunrpc layer
|
|
heuristically avoids overloading the CPU scheduler with too many
|
|
runnable nfsd threads. The ideal rate of change for this counter
|
|
is zero. Significant non-zero values indicate that the workload
|
|
is CPU limited. Usually this is associated with heavy CPU usage
|
|
on all the CPUs in the nfsd thread pool.
|
|
|
|
If a sustained large overloads-avoided rate is detected on a pool,
|
|
the top(1) utility should be used to check for the following
|
|
pattern of CPU usage on all the CPUs associated with the given
|
|
nfsd thread pool.
|
|
|
|
- %us ~= 0 (as you're *NOT* running applications on your NFS server)
|
|
|
|
- %wa ~= 0
|
|
|
|
- %id ~= 0
|
|
|
|
- %sy + %hi + %si ~= 100
|
|
|
|
If this pattern is seen, configuring more nfsd threads will *not*
|
|
improve the performance of the workload. If this patten is not
|
|
seen, then something more subtle is wrong.
|
|
|
|
threads-timedout
|
|
Counts how many times an nfsd thread triggered an idle timeout,
|
|
i.e. was not woken to handle any incoming network packets for
|
|
some time.
|
|
|
|
This statistic counts a circumstance where there are more nfsd
|
|
threads configured than can be used by the NFS workload. This is
|
|
a clue that the number of nfsd threads can be reduced without
|
|
affecting performance. Unfortunately, it's only a clue and not
|
|
a strong indication, for a couple of reasons:
|
|
|
|
- Currently the rate at which the counter is incremented is quite
|
|
slow; the idle timeout is 60 minutes. Unless the NFS workload
|
|
remains constant for hours at a time, this counter is unlikely
|
|
to be providing information that is still useful.
|
|
|
|
- It is usually a wise policy to provide some slack,
|
|
i.e. configure a few more nfsds than are currently needed,
|
|
to allow for future spikes in load.
|
|
|
|
|
|
Note that incoming packets on NFS transports will be dealt with in
|
|
one of three ways. An nfsd thread can be woken (threads-woken counts
|
|
this case), or the transport can be enqueued for later attention
|
|
(sockets-enqueued counts this case), or the packet can be temporarily
|
|
deferred because the transport is currently being used by an nfsd
|
|
thread. This last case is not very interesting and is not explicitly
|
|
counted, but can be inferred from the other counters thus:
|
|
|
|
packets-deferred = packets-arrived - ( sockets-enqueued + threads-woken )
|
|
|
|
|
|
More
|
|
----
|
|
Descriptions of the other statistics file should go here.
|
|
|
|
|
|
Greg Banks <gnb@sgi.com>
|
|
26 Mar 2009
|