Date: Tue, 16 Nov 2010 04:54:31 -0800 From: Jeremy Chadwick <freebsd@jdc.parodius.com> To: Christer Solskogen <christer.solskogen@gmail.com> Cc: freebsd-stable@freebsd.org, Ivan Voras <ivoras@freebsd.org> Subject: Re: "High" cpu usage when using ZFS cache device Message-ID: <20101116125431.GA90475@icarus.home.lan> In-Reply-To: <AANLkTi=tJ-Hf%2BrMqG0=tEzNV2jJW-B_7Yu_ftW4tAMqT@mail.gmail.com> References: <AANLkTinzwyhABYxzWknzRFzLCbcDSd3BU2kQ5tX_SSk-@mail.gmail.com> <20101116003029.GC79816@numachi.com> <AANLkTinfTgXzf7t3PtO2VAef7NSkKWc0RnGdpv=6_-Vj@mail.gmail.com> <ibtqvp$bfq$1@dough.gmane.org> <AANLkTi=tJ-Hf%2BrMqG0=tEzNV2jJW-B_7Yu_ftW4tAMqT@mail.gmail.com>
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On Tue, Nov 16, 2010 at 01:15:32PM +0100, Christer Solskogen wrote: > On Tue, Nov 16, 2010 at 12:47 PM, Ivan Voras <ivoras@freebsd.org> wrote: > > > You can easily test it - use the stick as a simple disk device with UFS and > > see how much CPU does it take simply to talk to the device. > > 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. > > See: > CPU: 0.0% user, 0.0% nice, 0.6% system, 0.0% interrupt, 99.3% idle > Mem: 832M Active, 960M Inact, 7017M Wired, 2600K Cache, 1237M Buf, 3063M Free > Swap: 8192M Total, 8192M Free > > PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU COMMAND > 38261 root 1 46 0 5776K 1112K wdrain 7 0:07 4.98% dd > > But when using it as cache device for zfs: > > CPU: 0.0% user, 0.0% nice, 11.9% system, 0.0% interrupt, 88.1% idle > Mem: 832M Active, 193M Inact, 5782M Wired, 2592K Cache, 1237M Buf, 5066M Free > Swap: 8192M Total, 8192M Free > > The funny thing is that when I add the device (and some cache is added > to it) the load is normal. But the load goes up when nothing is > written to it (or beeing read from it) Since you're running 8.1-RELEASE, can you please test this issue on RELENG_8 (8.1-STABLE) and see if it exists there? You can download a livefs snapshot or equivalent and test via that (preferably one which has ZFS v15 support; you'll need to make a new pool rather than upgrade your existing pool, unless you plan on moving to RELENG_8 permanently). Here's such a snapshot: ftp://ftp4.freebsd.org/pub/FreeBSD/snapshots/201011/ -- | 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 |
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