Thanks VERY MUCH to alan_at_nabeth.cxo.dec.com for his explanation of
the message "XPT Packet Pool LOW Water Mark Reached". His answer
is shown below. (I really need to look at uerf output more carefully.
It actually says it's a CAM entry.)
You're using the SCSI CAM driver. It used a fairly
complex memory management system for handling its
own internal data structures. The code would attempt
to keep a free list of data structures between a high
and low water mark. Too many and it would free the
structures to get under the high water mark. Too few
and it would allocate more to get above the low water
mark.
Since the driver was reasonably fast, this sort of complex
memory management was fine, except that the early versions
of the driver reported every instance that it went outside
the low and high water marks. Under very variable SCSI
I/O loads, this would cause flurries of the messages and
in extreme conditions, spend more time logging the status
than doing work.
If you only see a few of these, don't worry too much about
them. If they happen a lot, look at /sys/data/cam_data.c
to see if you can adjust the water marks to reduce the
frequency of the message. This was certainly fixed by
V4.4 and maybe V4.3A.
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Barbara Baker PHONE: (303) 861-6284
The Children's Hospital FAX: (303) 837-2577
Denver, Colorado Email: baker.barb_at_tchden.org
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Received on Fri Feb 28 1997 - 21:46:26 NZDT