Date: Mon, 8 Feb 2010 06:51:47 -0800 From: Jeremy Chadwick <freebsd@jdc.parodius.com> To: freebsd-stable@freebsd.org Subject: Re: ATA_CAM + ZFS gives short 1-2 seconds system freeze on disk load Message-ID: <20100208145147.GA3733@icarus.home.lan> In-Reply-To: <20100208143329.GA12057@megatron.madpilot.net> References: <20100208143329.GA12057@megatron.madpilot.net>
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On Mon, Feb 08, 2010 at 03:33:29PM +0100, Guido Falsi wrote: > Hi! > > I'm seeing this problem on my machine at work. It's an HP DC 7800, > mounts an ich9 chipset(not ahci capable). I'm attaching the dmesg. > > I noticed this in the past, but it got evident(and very annoying) > while recompiling many ports today after the jpeg-8 update. > > It looks like it freezes the system for the second or two it takes > to flush buffers to disk when there are big outputs. This happens > when decompressiong big distfiles, mainly. The openoffice port > triggers this almost continuosly every few seconds during compilation. > I've also seen this when working with big files(for example graphic > images in uncompressed formats). > > It gets very annoying and I don't remember this happening before > activating the ATA_CAM flag. There was some slowdown with big disk > access, but not a total freeze. This happens without ATA_CAM (e.g. using ataahci(4) or any other controller driver). The behaviour you're describing (bursty heavy disk I/O that stalls the subsystem) is pretty much the norm on all FreeBSD systems I've seen with ZFS. When it starts happening, it's easy to notice/follow using "zpool iostat 1" or "gstat -I500ms". Lots of I/O will happen (read or write) and the ARC is essentially being thrashed -- said utilities won't show any I/O counters incrementing until some threshold is reached, where you'll see a massive amount of I/O reported, during which time the system is sluggish (beyond acceptable levels, IMHO). A few seconds later, the I/O counters start reporting 0 as the ARC gets used, then a few seconds massive I/O, rinse lather repeat. I've seen Solaris 10 systems which behave the same way, and others which don't. I don't know what causes things to start behaving this way. > BTW there's another thing that shows up on this machine. Lately, this > too after putting the option ATA_CAM in the kernel, during boot there is > a long pause(exactly one minute, as the message below states) in this > point of the dmesg: This should probably be discussed in a different thread. -- | 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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