Date: Tue, 16 Nov 2010 17:48:31 +0100 From: Christer Solskogen <christer.solskogen@gmail.com> To: Alexander Leidinger <Alexander@leidinger.net> Cc: FreeBSD Stable <freebsd-stable@freebsd.org> Subject: Re: "High" cpu usage when using ZFS cache device Message-ID: <AANLkTikAP1ojwJH3k-tSbjJfdv6CSA5rc6wgwXZ6k9TA@mail.gmail.com> In-Reply-To: <20101116173111.10651nkzyneuy4m8@webmail.leidinger.net> References: <AANLkTinzwyhABYxzWknzRFzLCbcDSd3BU2kQ5tX_SSk-@mail.gmail.com> <20101116003029.GC79816@numachi.com> <AANLkTinfTgXzf7t3PtO2VAef7NSkKWc0RnGdpv=6_-Vj@mail.gmail.com> <ibtqvp$bfq$1@dough.gmane.org> <AANLkTi=tJ-Hf%2BrMqG0=tEzNV2jJW-B_7Yu_ftW4tAMqT@mail.gmail.com> <20101116135557.66601irt6kd1gndw@webmail.leidinger.net> <AANLkTimbtw-vnTwsywm2eeGK2qcAxggSA9ACL0HrufZm@mail.gmail.com> <20101116173111.10651nkzyneuy4m8@webmail.leidinger.net>
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On Tue, Nov 16, 2010 at 5:31 PM, Alexander Leidinger
<Alexander@leidinger.net> wrote:
> Quoting Christer Solskogen <christer.solskogen@gmail.com> (from Tue, 16 Nov
> 2010 14:00:48 +0100):
>
>> On Tue, Nov 16, 2010 at 1:55 PM, Alexander Leidinger
>> <Alexander@leidinger.net> wrote:
>>>
>>> How do you measure that nothing is read or written to it?
>>>
>>
>> I used zpool iostat -v
>
> "zpool iostat" (without -v) does not show cache filling writes to the cache
> device. I do not know about -v, but I would not be surprised if it does not
> show this too.
>
Ah, but it does.
capacity operations bandwidth
pool used avail read write read write
---------- ----- ----- ----- ----- ----- -----
data 2.11T 1.96T 0 0 0 0
raidz1 2.11T 1.96T 0 0 0 0
ada1 - - 0 0 0 0
ada2 - - 0 0 0 0
ada3 - - 0 0 0 0
cache - - - - - -
da0 2.64G 4.89G 0 0 0 0
---------- ----- ----- ----- ----- ----- -----
>>> Please check with
>>> gstat -f '^<DEVICE>$'
>>> if there are really no reads/writes to the device (please replace
>>> <DEVICE>
>>> with the name of your USB device, e.g. da0).
>>>
>>> If you see writes, I would say
>>> - this is the reason for the load
>>> - your cache is on the way to be filled with
>>> useful data
>>>
>>
>> I see almost no writes (nor reads)
>
> I'm not sure: you verified the output of "zpool iostat -v" with gstat or
> not? If not, please do.
>
Yeah, gstat shows (almost) the same as zpool iostat -v. (gstat have a
higher refresh rate than iostat)
> Based upon you other answer (with -H), I would still think the L2arc (cache)
> device is being filled in the background (which means there should be
> something visible with gstat).
>
gstat shows that something is going on when I add the cache
device(about one minute in my case). But the systemload is +0.01%. But
when it's settled the system load goes up.
top -HS says that the command called: l2arc_feed_threa goes up when
nothing is happening to the cache. (according to "zpool iostat -v"
and gstat)
--
chs,
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