Date: Wed, 29 Apr 2015 11:35:54 -0400
From: "J. Bruce Fields" <bfields@fieldses.org>
To: Scott Mayhew <smayhew@redhat.com>
Cc: linux-nfs@vger.kernel.org
Subject: Re: [PATCH] Documentation: remove overloads-avoided counter from
 knfsd-stats.txt
Message-ID: <20150429153554.GA18344@fieldses.org>
References: <1430318306-26029-1-git-send-email-smayhew@redhat.com>
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On Wed, Apr 29, 2015 at 10:38:26AM -0400, Scott Mayhew wrote:
> The 'overloads-avoided' counter itself was removed several years ago by
> commit 78c210e (Revert "knfsd: avoid overloading the CPU scheduler with
> enormous load averages").

Thanks for cleaning this up.--b.

> 
> Signed-off-by: Scott Mayhew <smayhew@redhat.com>
> ---
>  Documentation/filesystems/nfs/knfsd-stats.txt | 44 +++------------------------
>  1 file changed, 4 insertions(+), 40 deletions(-)
> 
> diff --git a/Documentation/filesystems/nfs/knfsd-stats.txt b/Documentation/filesystems/nfs/knfsd-stats.txt
> index 64ced51..1a5d821 100644
> --- a/Documentation/filesystems/nfs/knfsd-stats.txt
> +++ b/Documentation/filesystems/nfs/knfsd-stats.txt
> @@ -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
> -- 
> 1.9.3