strange system slowdown

Hello everyone,

for quiet a will I experience a strange system slowdowns. It looks like
system freezes for a moment and then continues to work. The most
noticeable result of this slowdown is sloppy mouse movement and skips in
sound card buffer updates (with nVidia graphics card driver loaded). It
can also be noticed when scrolling large amount of text in console (no x
started). Sound skips only in X and with nvidia proprietary driver,
there is no skips with Xorg nv driver (since it not installs interrupt
handler), but mouse cursor still moves sloopy.
The same problem present in FreeBSD 5.4-RELEASE.
There is no such a problem in Linux or Windows.

Hardware:
Foxconn i925X, 512Mb, iPentium4 530 (Prescott)_at_3000Ghz, HTT enabled,
GeForce 6600GT, SATA HDD.

The system is:
FreeBSD main.my.domain 6.0-CURRENT FreeBSD 6.0-CURRENT #0: Thu Jul  7
21:55:30 UTC 2005     root_at_main.my.domain:/usr/obj/usr/src/sys/BLACK
i386

Kernel config:
machine i386
cpu I686_CPU
ident BLACK

# To statically compile in device wiring instead of /boot/device.hints
#hints "GENERIC.hints" # Default places to look for devices.

#makeoptions DEBUG=-g # Build kernel with gdb(1) debug symbols

#options SCHED_ULE # ULE scheduler
options SCHED_4BSD # 4BSD scheduler
options PREEMPTION # Enable kernel thread preemption
options INET # InterNETworking
#options INET6 # IPv6 communications protocols
options FFS # Berkeley Fast Filesystem
options SOFTUPDATES # Enable FFS soft updates support
options UFS_ACL # Support for access control lists
options UFS_DIRHASH # Improve performance on big directories
#options MD_ROOT # MD is a potential root device
#options NFSCLIENT # Network Filesystem Client
#options NFSSERVER # Network Filesystem Server
#options NFS_ROOT # NFS usable as /, requires NFSCLIENT
#options MSDOSFS # MSDOS Filesystem
#options CD9660 # ISO 9660 Filesystem
options PROCFS # Process filesystem (requires PSEUDOFS)
options PSEUDOFS # Pseudo-filesystem framework
options GEOM_GPT # GUID Partition Tables.
options COMPAT_43 # Compatible with BSD 4.3 [KEEP THIS!]
options COMPAT_FREEBSD4 # Compatible with FreeBSD4
options SCSI_DELAY=5000 # Delay (in ms) before probing SCSI
options KTRACE # ktrace(1) support
options SYSVSHM # SYSV-style shared memory
options SYSVMSG # SYSV-style message queues
options SYSVSEM # SYSV-style semaphores
options _KPOSIX_PRIORITY_SCHEDULING # POSIX P1003_1B real-time
extensions
options KBD_INSTALL_CDEV # install a CDEV entry in /dev

options ADAPTIVE_GIANT # Giant mutex is adaptive.

# Debugging for use in -current
#options KDB # Enable kernel debugger support.
#options DDB # Support DDB.
#options GDB # Support remote GDB.
#options INVARIANTS # Enable calls of extra sanity checking
#options INVARIANT_SUPPORT # Extra sanity checks of internal structures,
required by INVARIANTS
#options WITNESS # Enable checks to detect deadlocks and cycles
#options WITNESS_SKIPSPIN # Don't run witness on spinlocks for speed

# To make an SMP kernel, the next two lines are needed
options SMP # Symmetric MultiProcessor Kernel
device apic # I/O APIC

# Bus support.  Do not remove isa, even if you have no isa slots
device isa
device pci

# Floppy drives
device fdc

# ATA and ATAPI devices
device ata
device atadisk # ATA disk drives
device ataraid # ATA RAID drives
device atapicd # ATAPI CDROM drives
device atapicam
options ATA_STATIC_ID # Static device numbering

# SCSI peripherals
device scbus # SCSI bus (required for SCSI)
device da # Direct Access (disks)
device cd # CD
device pass # Passthrough device (direct SCSI access)
#device ses # SCSI Environmental Services (and SAF-TE)

# atkbdc0 controls both the keyboard and the PS/2 mouse
device atkbdc # AT keyboard controller
device atkbd # AT keyboard
device psm # PS/2 mouse

device vga # VGA video card driver
options VESA

device splash # Splash screen and screen saver support

# syscons is the default console driver, resembling an SCO console
device sc
options SC_PIXEL_MODE

#device agp # support several AGP chipsets

# Floating point support - do not disable.
device npx

# Power management support (see NOTES for more options)
#device apm
# Add suspend/resume support for the i8254.
device pmtimer

# Serial (COM) ports
device sio # 8250, 16[45]50 based serial ports

# Parallel port
device ppc
device ppbus # Parallel port bus (required)
device lpt # Printer
device plip # TCP/IP over parallel
device ppi # Parallel port interface device
#device vpo # Requires scbus and da

# Pseudo devices.
device loop # Network loopback
device mem # Memory and kernel memory devices
device io # I/O device
device random # Entropy device
device ether # Ethernet support
device sl # Kernel SLIP
device ppp # Kernel PPP
device tun # Packet tunnel.
device pty # Pseudo-ttys (telnet etc)
device md # Memory "disks"
device gif # IPv6 and IPv4 tunneling
device faith # IPv6-to-IPv4 relaying (translation)

# The `bpf' device enables the Berkeley Packet Filter.
# Be aware of the administrative consequences of enabling this!
# Note that 'bpf' is required for DHCP.
device bpf # Berkeley packet filter

# USB support
device uhci # UHCI PCI->USB interface
device ohci # OHCI PCI->USB interface
device ehci # EHCI PCI->USB interface (USB 2.0)
device usb # USB Bus (required)
#device udbp # USB Double Bulk Pipe devices
device ugen # Generic
device uhid # "Human Interface Devices"
device ukbd # Keyboard
device ulpt # Printer
device umass # Disks/Mass storage - Requires scbus and da
device ums # Mouse
device urio # Diamond Rio 500 MP3 player
device uscanner # Scanners

device smb
device smbus
device ichsmb

The following device drivers are loaded:
2    3 0xc073d000 1cdcc    linux.ko
3    1 0xc075a000 8080     if_re.ko
4    2 0xc0763000 1aaf8    miibus.ko
5    1 0xc077e000 8088     snd_emu10k1.ko
6    2 0xc0787000 1f528    sound.ko
7    1 0xc07a7000 1d9c     cd9660_iconv.ko
8    6 0xc07a9000 49dc     libiconv.ko
9    2 0xc07ae000 8bec     cd9660.ko
10    1 0xc07b7000 8ec0     ng_ubt.ko
11    2 0xc07c0000 da3c     netgraph.ko
12    1 0xc07ce000 3c00c0   nvidia.ko
13   16 0xc0b8f000 5f450    acpi.ko
14    1 0xc1d7c000 2000     ntfs_iconv.ko
15    1 0xc1d7e000 b000     ntfs.ko
16    1 0xc1dfd000 2000     msdosfs_iconv.ko
17    1 0xc1e02000 e000     msdosfs.ko
18    1 0xc1f93000 2000     blank_saver.ko
19    1 0xc1ff6000 2000     rtc.ko

With best regards,
Vladimir Novoseltsev