Date: Tue, 16 Nov 2010 13:59:09 +0100 From: Ivan Voras <ivoras@freebsd.org> To: Christer Solskogen <christer.solskogen@gmail.com> Cc: freebsd-stable@freebsd.org Subject: Re: "High" cpu usage when using ZFS cache device Message-ID: <AANLkTinaB9b4CD-xDKFNMF7_4%2B%2Bmhs0GCwzv_cyiW=Gc@mail.gmail.com> 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 16 November 2010 13:15, Christer Solskogen <christer.solskogen@gmail.com> 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=3D/dev/zero of=3D/mnt/file". > The systemload goes +0.6 instead if +10.3. > > See: > CPU: =C2=A00.0% user, =C2=A00.0% nice, =C2=A00.6% system, =C2=A00.0% inte= rrupt, 99.3% idle > Mem: 832M Active, 960M Inact, 7017M Wired, 2600K Cache, 1237M Buf, 3063M = Free > Swap: 8192M Total, 8192M Free > > =C2=A0PID USERNAME =C2=A0 =C2=A0THR PRI NICE =C2=A0 SIZE =C2=A0 =C2=A0RES= STATE =C2=A0 C =C2=A0 TIME =C2=A0 WCPU COMMAND > 38261 root =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A01 =C2=A046 =C2=A0 =C2=A00 = =C2=A05776K =C2=A01112K wdrain =C2=A07 =C2=A0 0:07 =C2=A04.98% dd > > But when using it as cache device for zfs: > > CPU: =C2=A00.0% user, =C2=A00.0% nice, 11.9% system, =C2=A00.0% 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) You mean you have system load on an otherwise idle system? Try this: 1) start "top" with parameters -H -S, see if anything is using the CPU time 2) start "gstat", see if anything is using IO, and if it's particularly slow or busying the device too much
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