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Date: Tue, 16 Nov 2010 08:01:50 -0800
From: Jeremy Chadwick <freebsd@jdc.parodius.com>
To: Christer Solskogen <christer.solskogen@gmail.com>
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Cc: freebsd-stable@freebsd.org
Subject: Re: "High" cpu usage when using ZFS cache device
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On Tue, Nov 16, 2010 at 04:53:57PM +0100, Christer Solskogen wrote:
> On Tue, Nov 16, 2010 at 2:11 PM, Ollivier Robert
> <roberto@keltia.freenix.fr> wrote:
> > According to Christer Solskogen:
> >> See, that is why I think it is a ZFS issue. Because I did that.
> >> I created a UFS filesystem on the same usb stick. Mounted it and did a
> >> "dd if=/dev/zero of=/mnt/file".
> >> The systemload goes +0.6 instead if +10.3.
> >
> > Do not forget that everything that is read/written from/to USB devices goes through the CPU (no DMA or anything for USB devices).
> >
> 
> I didn't forget that. Thats why I also tested with UFS. And I do not
> have the same issue with that.
> 
> With top -HS I discovered this:
>     5 root        -8    -     0K    76K zio->i  4 403.2H 85.06%
> {l2arc_feed_threa}

Please provide the output from:

sysctl -a | grep vfs.zfs.arc
sysctl -a | grep vm.kmem
sysctl kstat.zfs.misc.arcstats

Thank you.

-- 
| Jeremy Chadwick                                   jdc@parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |