linux-kernel - Re: VM issue causing high CPU loads

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Date:	Wed, 2 Sep 2009 17:06:42 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Yohan <ytordjman@...p.free.fr>
Cc:	ytordjman@...p.free.fr, linux-kernel@...r.kernel.org,
	linux-nfs@...r.kernel.org, Neil Brown <neilb@...e.de>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Trond Myklebust <trond.myklebust@....uio.no>, mikevs@...all.net
Subject: Re: VM issue causing high CPU loads

On Mon, 31 Aug 2009 22:39:20 +0200
Yohan <ytordjman@...p.free.fr> wrote:

> Yohan wrote:
> > Andrew Morton wrote:
> >> On Mon, 24 Aug 2009 16:23:22 +0200
> >> Yohan <kernel@...an.staff.proxad.net> wrote:  
> >>> Hi,
> >>>
> >>>     Is someone have an idea for that :
> >>>
> >>>         http://bugzilla.kernel.org/show_bug.cgi?id=14024
> >>>     
> >> Please generate a kernel profile to work out where all the CPU tie is
> >> being spent.  Documentation/basic_profiling.txt is a starting point.
> >>   
> > I post some new reports, it seems that the problem is in  
> > rpcauth_lookup_credcache ...

Thanks, that helps a lot.

> > for information, this is an imap mail server that mounts ~10 netapp 
> > over ~300 mountpoints..
>     I saw that : http://patchwork.kernel.org/patch/24747/

I wonder what happened with Miquel's patch?

> I did only:
> 
> --- linux-2.6.27.21/include/linux/sunrpc/auth.h	2009-03-23 23:04:09.000000000 +0100
> +++ linux-2.6.27.21/include/linux/sunrpc/auth.h	2009-05-19 16:02:35.000000000 +0200
> @@ -62,8 +62,12 @@ 
>   */
> - #define RPC_CREDCACHE_HASHBITS	4
> + #define RPC_CREDCACHE_HASHBITS	12
> 
> 
> And i test it in prod since sunday: i only have 36% of one core used by 
> system
> versus more than 3 cores used by system in another server that did a 
> drop_caches at morning...
> 

OK, but it's still pretty bad.  Let's tell the NFS guys.

In http://bugzilla.kernel.org/show_bug.cgi?id=14024 we appear to have a
major meltdown caused by the linear search in
rpcauth_lookup_credcache() with Yohan's workload.

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