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Commit 72faedae authored by Scott Mayhew's avatar Scott Mayhew Committed by J. Bruce Fields
Browse files

Documentation: remove overloads-avoided counter from knfsd-stats.txt 



The 'overloads-avoided' counter itself was removed several years ago by
commit 78c210ef (Revert "knfsd: avoid overloading the CPU scheduler with
enormous load averages").

Signed-off-by: default avatarScott Mayhew <smayhew@redhat.com>
Signed-off-by: default avatarJ. Bruce Fields <bfields@redhat.com>
parent fd891454

Documentation/filesystems/nfs/knfsd-stats.txt

+4 −40
Original line number Diff line number Diff line
@@ -68,16 +68,10 @@ sockets-enqueued 
	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.

	This can happen because there are too few nfsd threads in the thread

	pool for the NFS workload (the workload is thread-limited), in which

	case configuring more nfsd threads will probably improve the

	performance of the NFS workload.



threads-woken

	Counts how many times an idle nfsd thread is woken to try to
@@ -88,36 +82,6 @@ threads-woken 
	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