Kernel preemption leads to SATA instability (how to debug?)

[Daniel Eriksson]

Hi, I'm getting SATA instability on my system with kernel preemption
enabled. When accessing the SATA discs at the same time as other discs (for
example during a fsck of all file systems on the machine) it only takes a
few seconds for the SATA discs to start reporting things like this:

Interrupt storm detected on "irq20: atapci4"; throttling interrupt source
ad20: FAILURE - already active DMA on this device
ad20: setting up DMA failed

This is on a recent kernel (2004.07.18.05.00.00), but it's been like this
ever since the kernel preemption stuff was turned on again a few weeks ago.
With preemption disabled (by editing param.h) the system seems to be stable,
but somewhat sluggish (a simple bzip2 compress operation can generate a load
average of 10+).

How would I go about debugging this? Any hints would be appreciated. I do
have KDB/DDB and debug symbols compiled in, but the machine is a production
machine so I cannot afford long debugging sessions unfortunately.

Attached is the dmesg.boot and kernel config file. Below are some settings
that might be interesting from other files:

/etc/sysctl.conf
----------------
kern.ipc.maxsockbuf=524288
kern.ipc.somaxconn=1024
kern.maxfiles=16384
kern.polling.enable=1
kern.polling.idle_poll=0
kern.polling.burst_max=200
kern.polling.each_burst=25
kern.polling.poll_in_trap=1
net.inet.tcp.sendspace=262144
net.inet.tcp.recvspace=262144
net.inet.tcp.rfc3390=1
net.inet.tcp.inflight_enable=1
net.inet.tcp.inflight_min=6144
net.inet.tcp.inflight_debug=0
net.inet.tcp.sack.enable=1
net.inet.ip.intr_queue_maxlen=500

/boot/loader.conf
-----------------
kern.ipc.nmbclusters="16384"
hw.apic.mixed_mode=0
hw.intr_storm_threshold=5000

/etc/make.conf
--------------
CFLAGS= -O2 -pipe -fno-builtin
COPTFLAGS= -O2 -pipe -fno-builtin
CPUTYPE?=athlon-xp


/Daniel Eriksson
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