Date: Tue, 21 Dec 1999 11:01:50 +1030 From: Greg Lehey <grog@lemis.com> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: FreeBSD current users <FreeBSD-current@FreeBSD.ORG> Subject: Re: Recent current hangs frequently for 1 to 2 seconds. Message-ID: <19991221110148.N440@freebie.lemis.com> In-Reply-To: <199912210019.QAA62510@apollo.backplane.com> References: <19991219143759.C465@freebie.lemis.com> <199912190416.UAA01125@apollo.backplane.com> <19991221095213.L440@freebie.lemis.com> <199912210019.QAA62510@apollo.backplane.com>
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On Monday, 20 December 1999 at 16:19:06 -0800, Matthew Dillon wrote:
>
> :Thanks. I've put in the patch, but I'm still seeing the problems. It
> :seems to be related to SCSI activity (I'm currently performing a
> :backup on a DLT drive, and apart from that very little disk I/O). Any
> :other ideas? It seems to me as if the whole system freezes
> :(keystrokes don't echo, for example), so possibly something is going
> :into splhigh for too long.
> :
> :Greg
>
> No, this is very odd. Certainly reading from disk should not
> cause any blockages. But DLT & SCSI -- there are lots of possiblities
> there. Is the DLT device sharing the same SCSI bus as the
> disks?
Yes.
> I've historically had bad luck with a shared arrangement and now
> always put SCSI tape units on their own SCSI bus.
For other reasons, I intend to do just this, though I'm not sure it's
a good idea: for one thing, I don't have any spare PCI slots, so it
will have to be a 1542B. But it will be worth checking.
It's possible you might be on to something. I've been running iostat
at 1 second intervals, and during the last hang I saw:
tty ad2 da1 sa1 cpu
tin tout KB/t tps MB/s KB/t tps MB/s KB/t tps MB/s us ni sy in id
36 142 7.75 95 0.72 0.00 0.00 0 10.00 27 0.27 29 0 9 1 61
21 142 8.00 69 0.54 0.00 0.00 0 0.00 0 0.00 6 0 1 0 93
37 143 8.00 44 0.34 0.00 8.00 3 0.00 0 0.00 5 0 1 1 94
41 142 1.76 106 0.18 16.00 5.25 4 10.00 14 0.13 24 0 18 0 57
15 143 1.98 87 0.17 0.00 0.00 0 10.00 16 0.15 30 0 15 2 54
Note that the stop in tape activity corresponds with a start in disk
activity. I'll keep an eye on that and see if it looks the same the
next time.
> If the SCSI bus is hanging something should show up in the kernel logs
> or dmesg output.
Right. But there's nothing there.
> Another possibility is that the SCSI operation is causing a hangup or
> bringing out a bug in the networking somewhere. A lockup for a second
> or two could be an indication of packet loss. Haven't there been a
> couple of mbuf-related commits recently? It would be something to look
> review, anyway.
I don't see any evidence of network participation. All the activity
here is local.
Greg
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