Environment:
4.4 PRERELEASE
CPU: Pentium III/Pentium III Xeon/Celeron (701.59-MHz 686-class CPU)
real memory = 536805376 (524224K bytes)
Adaptec 2940 Ultra2 SCSI adapter
4 x FUJITSU MAE3091LC LVD disks
Kernel config is more-or-less GENERIC, with maxusers set to 256 and
some unneeded drivers removed.
Problem:
A particular process that does a large amount of lseeks and small writes
to a large (~1Gb) file causes other processes to block for many (>10) seconds
at times.
Analysing the problem, it appears that the offending process manages to
very quickly dirty a large number of buffers, then enters the "flswai"
state (as reported by "top"), flushing dirty buffers to disk, and during
the flushing frenzy, all other processes seem to block. The interesting
thing is that the offending process's I/O is to a disk that is unused by
any other process. At the same time, disk I/O on the other disks is nil,
or negligible. There is no paging activity and masses of free memory.
During the flushing period, the CPU usage (as reported bu systat) drops
to < 1%.
I've recreated the environment on a spare machine that is otherwise idle,
and is easily repeatable.
This situation has arisen while attempting to migrate an application
from BSD/OS 4.1 to FreeBSD. The symptoms don't occur on BSD/OS.
I'm more than happy to experiment with any suggestions to overcome this
issue.
--
Richard Perini Internet: [EMAIL PROTECTED]
Corinthian Engineering Pty Ltd PHONE: +61 2 9906 7866
Sydney, Australia FAX: +61 2 9906 2464
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