Date: Thu, 7 Jan 2016 12:49:15 -0800 From: Mark Millard <markmi@dsl-only.net> To: Hans Petter Selasky <hps@selasky.org>, Ian Lepore <ian@freebsd.org> Cc: freebsd-arm <freebsd-arm@freebsd.org> Subject: Re: FYI: various 11.0-CURRENT -r293227 (and older) hangs on arm (rpi2): a description of sorts Message-ID: <1E15506E-2CE4-41E8-98D5-05F9AB031F1C@dsl-only.net> In-Reply-To: <8B728C93-9C90-4821-A607-5D157F028812@dsl-only.net> References: <E0379BE9-308A-4219-A8AE-A5FFE828BA93@dsl-only.net> <1452183170.1215.4.camel@freebsd.org> <FB0D5486-AD27-44A7-86CA-68989AE08EC7@dsl-only.net> <1452196099.1215.12.camel@freebsd.org> <568EC4D8.7010106@selasky.org> <8B728C93-9C90-4821-A607-5D157F028812@dsl-only.net>
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On 2016-Jan-7, at 12:20 PM, Mark Millard <markmi at dsl-only.net> wrote: > On 2016-Jan-7, at 12:04 PM, Hans Petter Selasky <hps at selasky.org> = wrote: >>=20 >> On 01/07/16 20:48, Ian Lepore wrote: >>> If the filesystems and swap space are on a usb drive, then maybe = it's >>> the usb subsystem that's hanging. The wait states you showed for = those >>> processes are consistant with what I've seen when all buffers get >>> backed up in a queue on one non-responsive or slow device. It may = be >>> that there's a way to get the system deadlocked when it's low on >>> buffers and there is memory pressure causing the swap to be used (I >>> generally run arms systems without any swap configured). >>>=20 >>> Running gstat in another window while this is going on may give you >>> some insight into the situation. Beyond that I don't know what to = look >>> at, especially since you generally can't launch any new tools once = the >>> system gets into this kind of state. gstat shows everything zero during a hang, even L(q) column. (Length of = queue?) I used: gstat -cod and had it running over the serial console port during the attempted = portmaster activity. >>> -- Ian >>=20 >> Hi, >>=20 >> All USB transfers towards disk devices have timeouts, so if something = is hanging at USB level, you'll get a printout eventually. >=20 > What sort of timescale after deadlock/live-lock is observed to = apparently have started does one have to wait in order to conclude that = the timeouts would have happened and so they do not apply to the = deadlock/live-lock? >=20 >> The USB kernel processes needed for doing I/O transfers are not = pinned to RAM. Can it happen if a USB process is swapped to disk, that = the system cannot wakeup a swapped out process to get more swap? >>=20 >> --HPS >=20 > Wow. Could I use ddb to somehow check on the "USB kernel processes" = swap status when the overall context is deadlocked/live-locked? If yes, = how? Otherwise something in top or some such display that I'd left = running over the serial console would have to present useful information = on the subject. Is there anything that would? >=20 =3D=3D=3D Mark Millard markmi at dsl-only.net
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