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SubjectReproducible SMP/SCSI Hangs under 2.0.xx
Date
From


I have enclosed some routines which will reproducibly hang a
2.0.xx/SMP box running SCSI. It has been tested with NCR and Buslogic
controllers. Here is the README:


This is code that tickles a bug under SMP/SCSI linux 2.0.27 (and
earlier 2.0.xx revs) which causes the machine to hang. There are two
programs, db_create, which creates a large file (of size `cat size`
Mb) of zeroes, and load, which mmaps the file and repeatedly does both
sequential and random seeks on it (consequently beating the heck out
of both the memory and disk systems). We find that the hang is easiest
to reproduce when 'size' is 2-3X physical memory. For an 8M system,
30M is adequate. A trick we use is to put 'append mem=8M' in the
lilo.conf. For our full configuration (64M), we needed 'size' around
200M.

Build the programs by typing `make'. To reproduce the hang, first fire
up the RUN_ON_VC1 script, which creates a file, foo, (default size:
30M) and then runs load on it. On another virtual console, run the
RUN_ON_VC2 script, which first sleeps 20 seconds and then repeatedly
creates another file, foo1, (default size: 30M). After a few minutes,
all of the disk lights go off and the machine hangs, requiring a hard
reset. Note that we do not see the hang as often if we omit the
sleep.

We have observed this problem on two of our systems, a dual processor
AMI Goliath PPro200/512k system, and a dual processor SuperMicro P6DOF
PPro200/512k. We were able to reproduce the hang with kernel versions back
to 2.0.14. We have observed it with both a BusLogic BT958 SCSI controller
and a Symbios (NCR) 53C825 SCSI controller using the BSD driver. We did
not observe a hang with the Eckhardt NCR driver. We do not observe the
problem if we have compiled the kernel single processor. We can reduce the
frequency of the hangs (i.e. you have to run the db_create script many
more times on a loaded machine to get the hang) by: 1) Installing Alan
Cox's irq forwarding patches or 2) Either reducing the tagged queueing
depth with the BusLogic, or disabling tagged queueing altogether. We have
not observed the hang on machines which have disabled tagged queueing
and use the forwarding patches, although we have not run long enough
tests to see if the problem has gone away entirely.

Any help with this problem would be greatly appreciated.

Bill Reynolds
bill@santafe.edu

=================
Bill Reynolds
bill@santafe.edu


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/%53P9X#_`L98T8(`4```
`
end

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