Date: Mon, 14 Sep 2009 08:15:07 -0500 From: Guy Helmer <ghelmer@palisadesys.com> To: Linda Messerschmidt <linda.messerschmidt@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: Intermittent system hangs on 7.2-RELEASE-p1 Message-ID: <4AAE41DB.9050104@palisadesys.com> In-Reply-To: <237c27100909112147h64f71585p2a97f2b48a510985@mail.gmail.com> References: <237c27100908261203g7e771400o2d9603220d1f1e0b@mail.gmail.com> <200909111102.14503.jhb@freebsd.org> <237c27100909111035y544e8c91hc7726fd6ef16e351@mail.gmail.com> <200909111506.47309.jhb@freebsd.org> <237c27100909111905y244924c1n93b4e4d9ceda44be@mail.gmail.com> <237c27100909112055i35612b4btbfbecb8b5dd1568c@mail.gmail.com> <4AAB1E34.2060908@elischer.org> <237c27100909112147h64f71585p2a97f2b48a510985@mail.gmail.com>
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Linda Messerschmidt wrote: > Well, this is interesting. I got really frustrated with the other > approach, so I thought I'd thin a machine down absolutely as far as I > could, eliminate every possible source of delay, and see what happens. > I killed everything... cron, RPC, NFS, devd, gmon, nrpe, everything. > The Apache and its exerciser are now the only things running on the > machine, and the Apache is only touching an md0 swap device mounted on > /mnt. I *still* get the hangs. > > It hangs for all sorts of different periods, but the duration of the > stall is approximately inversely proportional to the chance of seeing > it. To get a short delay, you need wait only a little bit. If you > want a 2-3 second delay, you may have to wait 15-20 minutes. > On what sort of hardware is this hang occurring? Several months ago I was trying to resolve an intermittent hang under FreeBSD 7. I collected a large number of crashdumps I created using the kernel debugger when I caught the machine hanging, but the backtraces were very inconsistent, and the hang was only occurring on Xeons with multithreading (older 2.8GHz and 3.6GHz Xeons). I was able to prevent the hang by setting "mach.hyperthreading_enabled=0" in /boot/loader.conf, but I am still not sure why it worked. Guy
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