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$1@dough.gmane.org> <AANLkTi=tJ-Hf%2BrMqG0=tEzNV2jJW-B_7Yu_ftW4tAMqT@mail.gmail.com> <20101116135557.66601irt6kd1gndw@webmail.leidinger.net> <AANLkTimbtw-vnTwsywm2eeGK2qcAxggSA9ACL0HrufZm@mail.gmail.com> <20101116173111.10651nkzyneuy4m8@webmail.leidinger.net>
next in thread | previous in thread | raw e-mail | index | archive | help
On Tue, Nov 16, 2010 at 5:31 PM, Alexander Leidinger <Alexander@leidinger.net> wrote: > Quoting Christer Solskogen <christer.solskogen@gmail.com> (from Tue, 16 N= ov > 2010 14:00:48 +0100): > >> On Tue, Nov 16, 2010 at 1:55 PM, Alexander Leidinger >> <Alexander@leidinger.net> wrote: >>> >>> How do you measure that nothing is read or written to it? >>> >> >> I used zpool iostat -v > > "zpool iostat" (without -v) does not show cache filling writes to the cac= he > device. I do not know about -v, but I would not be surprised if it does n= ot > show this too. > Ah, but it does. capacity operations bandwidth pool used avail read write read write ---------- ----- ----- ----- ----- ----- ----- data 2.11T 1.96T 0 0 0 0 raidz1 2.11T 1.96T 0 0 0 0 ada1 - - 0 0 0 0 ada2 - - 0 0 0 0 ada3 - - 0 0 0 0 cache - - - - - - da0 2.64G 4.89G 0 0 0 0 ---------- ----- ----- ----- ----- ----- ----- >>> Please check with >>> =A0gstat -f '^<DEVICE>$' >>> 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 >>> =A0- this is the reason for the load >>> =A0- your cache is on the way to be filled with >>> =A0 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 (cac= he) > 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) --=20 chs,
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?AANLkTikAP1ojwJH3k-tSbjJfdv6CSA5rc6wgwXZ6k9TA>