Hello,

I have been noticing some disturbing patterns on two different machines
I'm trying NetBSD on.  When I am untarring a file, or generally doing
anything that is causing large amounts of data to be written at once,
interactive performance is seriously degraded.  For instance, while I
was unpacking pkgsrc.tar.gz once, I had /etc/group open in vi.  Saving
that file took approximately 20 seconds.

I have observed this behavior on two systems:

* K6-3 400MHz, Ultra/33 and Ultra/133 IDE disks

* P4 800MHz, SCSI (AHA-2940)

Both systems also run Linux on the same hardware (the first on the same
disks even) and do not exhibit the problems under Linux.

At first, I suspected the problem was the IDE, but when I noticed the
problem on the SCSI machine as well, that made me wonder if there was
something else at fault.

It seems like when this problem occurs, an I/O scheduler somewhere is
starving everything but the big writing process of resources.  But I
have no idea if this is tweakable somewhere, or how to go about fixing
it.

This is NetBSD 1.6.1.  Both systems are running ffs with softdep
enabled (though I believe the problem existed without softdep as well).

Thanks,
John Goerzen