Date: Tue, 16 Nov 2010 17:31:11 +0100 From: Alexander Leidinger <Alexander@Leidinger.net> 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: <20101116173111.10651nkzyneuy4m8@webmail.leidinger.net> In-Reply-To: <AANLkTimbtw-vnTwsywm2eeGK2qcAxggSA9ACL0HrufZm@mail.gmail.com> References: <AANLkTinzwyhABYxzWknzRFzLCbcDSd3BU2kQ5tX_SSk-@mail.gmail.com> <20101116003029.GC79816@numachi.com> <AANLkTinfTgXzf7t3PtO2VAef7NSkKWc0RnGdpv=6_-Vj@mail.gmail.com> <ibtqvp$bfq$1@dough.gmane.org> <AANLkTi=tJ-Hf%2BrMqG0=tEzNV2jJW-B_7Yu_ftW4tAMqT@mail.gmail.com> <20101116135557.66601irt6kd1gndw@webmail.leidinger.net> <AANLkTimbtw-vnTwsywm2eeGK2qcAxggSA9ACL0HrufZm@mail.gmail.com>
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Quoting Christer Solskogen <christer.solskogen@gmail.com> (from Tue, =20 16 Nov 2010 14:00:48 +0100): > On Tue, Nov 16, 2010 at 1:55 PM, Alexander Leidinger > <Alexander@leidinger.net> wrote: >> How do you measure that nothing is read or written to it? >> > > I used zpool iostat -v "zpool iostat" (without -v) does not show cache filling writes to the =20 cache device. I do not know about -v, but I would not be surprised if =20 it does not show this too. >> Please check with >> =C2=A0gstat -f '^<DEVICE>$' >> if there are really no reads/writes to the device (please replace <DEVIC= E> >> with the name of your USB device, e.g. da0). >> >> If you see writes, I would say >> =C2=A0- this is the reason for the load >> =C2=A0- your cache is on the way to be filled with >> =C2=A0 useful data >> > > I see almost no writes (nor reads) I'm not sure: you verified the output of "zpool iostat -v" with gstat =20 or not? If not, please do. >> If gstat shows zero activity, I suggest to run 'top -S' and look at the >> process(es) which consume about 10% CPU (do not take care about the idle >> process). Based upon this we can maybe suggest further things to >> investigate. >> > > Heres the output of that: > CPU: 0.0% user, 0.0% nice, 11.8% system, 0.0% interrupt, 88.1% idle > Mem: 841M Active, 193M Inact, 5086M Wired, 4876K Cache, 1237M Buf, 5750M = Free > Swap: 8192M Total, 8192M Free > > PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU COMM= AND > 11 root 8 171 ki31 0K 128K CPU0 0 ??? 713.62% idl= e > 5 root 5 -8 - 0K 76K zvol:i 5 401.9H 91.16% zfsk= ern > > Thanks for your time on looking into this :-) Based upon you other answer (with -H), I would still think the L2arc =20 (cache) device is being filled in the background (which means there =20 should be something visible with gstat). Bye, Alexander. --=20 Sorry never means having you're say to love. http://www.Leidinger.net Alexander @ Leidinger.net: PGP ID =3D B0063FE7 http://www.FreeBSD.org netchild @ FreeBSD.org : PGP ID =3D 72077137
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