Disk performance hit with Dom0 vs native?

[Stephen Borrill <netbsd%precedence.co.uk@localhost>]

With an IBM x206 and 3.0_BETA as of about a week ago, I see a very big
difference in apparent disk write performance between dom0 and booting 
from a GENERIC kernel.

Using "dd if=/dev/zero of=/dev/rwd1d bs=1m", I get about 11MB/s under Xen, 
but 59MB/s with GENERIC. Is such a difference to be expected?

GENERIC dmesg below:

NetBSD 3.0_BETA (GENERIC) #0: Tue Nov  8 07:36:29 UTC 2005
        
builds%b2.netbsd.org@localhost:/home/builds/ab/netbsd-3/i386/200511080000Z-obj/home/builds/ab/netbsd-3/src/sys/arch/i386/compile/GENERIC
total memory = 1023 MB
avail memory = 993 MB
BIOS32 rev. 0 found at 0xfd5b6
mainbus0 (root)
cpu0 at mainbus0: (uniprocessor)
cpu0: Intel (686-class), 3000.68 MHz, id 0xf41
cpu0: features bfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR>
cpu0: features bfebfbff<PGE,MCA,CMOV,PAT,PSE36,CFLUSH,DS,ACPI,MMX>
cpu0: features bfebfbff<FXSR,SSE,SSE2,SS,HTT,TM,SBF>
cpu0: features2 441d<SSE3,MONITOR,DS-CPL,CID,xTPR>
cpu0: "Intel(R) Pentium(R) 4 CPU 3.00GHz"
cpu0: I-cache 12K uOp cache 8-way
cpu0: L2 cache 1 MB 64B/line 8-way
cpu0: ITLB 4K/4M: 64 entries
cpu0: DTLB 4K/4M: 64 entries
cpu0: running without thermal monitor!
cpu0: 32 page colors
pci0 at mainbus0 bus 0: configuration mode 1
pci0: i/o space, memory space enabled, rd/line, rd/mult, wr/inv ok
pchb0 at pci0 dev 0 function 0
pchb0: Intel 82875P Host (rev. 0x02)
ppb0 at pci0 dev 3 function 0: Intel 82875P PCI-CSA Bridge (rev. 0x02)
pci1 at ppb0 bus 2
pci1: i/o space, memory space enabled
wm0 at pci1 dev 1 function 0: Intel i82547GI 1000BASE-T Ethernet, rev. 0
wm0: interrupting at irq 5
wm0: Communication Streaming Architecture
wm0: 65536 word (16 address bits) SPI EEPROM
wm0: Ethernet address 00:11:25:ac:11:33
igphy0 at wm0 phy 1: Intel IGP01E1000 Gigabit PHY, rev. 0
igphy0: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, 1000baseT, 
1000baseT-FDX, auto
ppb1 at pci0 dev 28 function 0: Intel 6300ESB PCI-X Bridge (rev. 0x02)
pci2 at ppb1 bus 3
pci2: i/o space, memory space enabled, rd/line, wr/inv ok
uhci0 at pci0 dev 29 function 0: Intel 6300ESB USB UHCI Controller (rev. 0x02)
uhci0: interrupting at irq 11
usb0 at uhci0: USB revision 1.0
uhub0 at usb0
uhub0: Intel UHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub0: 2 ports with 2 removable, self powered
uhci1 at pci0 dev 29 function 1: Intel 6300ESB USB UHCI Controller (rev. 0x02)
uhci1: interrupting at irq 5
usb1 at uhci1: USB revision 1.0
uhub1 at usb1
uhub1: Intel UHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub1: 2 ports with 2 removable, self powered
Intel 6300ESB Watchdog Timer (miscellaneous system, revision 0x02) at pci0 dev 
29 function 4 not configured
Intel 6300ESB Advanced Interrupt Controller (interrupt system, interface 0x20, 
revision 0x02) at pci0 dev 29 function 5 not configured
ehci0 at pci0 dev 29 function 7: Intel 6300ESB USB EHCI Controller (rev. 0x02)
ehci0: interrupting at irq 11
ehci0: EHCI version 1.0
ehci0: companion controllers, 2 ports each: uhci0 uhci1
usb2 at ehci0: USB revision 2.0
uhub2 at usb2
uhub2: Intel EHCI root hub, class 9/0, rev 2.00/1.00, addr 1
uhub2: single transaction translator
uhub2: 4 ports with 4 removable, self powered
ppb2 at pci0 dev 30 function 0: Intel 82801BA Hub-PCI Bridge (rev. 0x0a)
pci3 at ppb2 bus 4
pci3: i/o space, memory space enabled
vga1 at pci3 dev 2 function 0: ATI Technologies Radeon 7000/VE (rev. 0x00)
wsdisplay0 at vga1 kbdmux 1: console (80x25, vt100 emulation)
wsmux1: connecting to wsdisplay0
Conexant Systems product 0x8800 (video multimedia, revision 0x05) at pci3 dev 8 
function 0 not configured
Conexant Systems product 0x8802 (miscellaneous multimedia, revision 0x05) at 
pci3 dev 8 function 2 not configured
Conexant Systems product 0x8804 (miscellaneous multimedia, revision 0x05) at 
pci3 dev 8 function 4 not configured
pcib0 at pci0 dev 31 function 0
pcib0: Intel 6300ESB LPC Interface Bridge (rev. 0x02)
piixide0 at pci0 dev 31 function 2
piixide0: Intel 6300ESB Serial ATA Controller (rev. 0x02)
piixide0: bus-master DMA support present
piixide0: primary channel configured to compatibility mode
piixide0: primary channel interrupting at irq 14
atabus0 at piixide0 channel 0
piixide0: secondary channel configured to compatibility mode
piixide0: secondary channel interrupting at irq 15
atabus1 at piixide0 channel 1
Intel 6300ESB SMBus Controller (SMBus serial bus, revision 0x02) at pci0 dev 31 
function 3 not configured
isa0 at pcib0
lpt0 at isa0 port 0x378-0x37b irq 7
com0 at isa0 port 0x3f8-0x3ff irq 4: ns16550a, working fifo
com1 at isa0 port 0x2f8-0x2ff irq 3: ns16550a, working fifo
pckbc0 at isa0 port 0x60-0x64
pckbd0 at pckbc0 (kbd slot)
pckbc0: using irq 1 for kbd slot
wskbd0 at pckbd0: console keyboard, using wsdisplay0
pms0 at pckbc0 (aux slot)
pckbc0: using irq 12 for aux slot
wsmouse0 at pms0 mux 0
pcppi0 at isa0 port 0x61
midi0 at pcppi0: PC speaker
sysbeep0 at pcppi0
isapnp0 at isa0 port 0x279: ISA Plug 'n Play device support
npx0 at isa0 port 0xf0-0xff: using exception 16
fdc0 at isa0 port 0x3f0-0x3f7 irq 6 drq 2
isapnp0: no ISA Plug 'n Play devices found
fd0 at fdc0 drive 0: 1.44MB, 80 cyl, 2 head, 18 sec
Kernelized RAIDframe activated
atapibus0 at atabus0: 2 targets
cd0 at atapibus0 drive 0: <PIONEER DVD-RW  DVR-110D, EIDC337852WL, 1.17> cdrom 
removable
cd0: 32-bit data port
cd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 4 (Ultra/66)
cd0(piixide0:0:0): using PIO mode 4, Ultra-DMA mode 4 (Ultra/66) (using DMA)
wd0 at atabus1 drive 0: <Maxtor 6Y160M0>
wd0: drive supports 16-sector PIO transfers, LBA48 addressing
wd0: 149 GB, 310101 cyl, 16 head, 63 sec, 512 bytes/sect x 312581808 sectors
wd0: 32-bit data port
wd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 6 (Ultra/133)
wd1 at atabus1 drive 1: <Maxtor 6Y080M0>
wd1: drive supports 16-sector PIO transfers, LBA addressing
wd1: 78167 MB, 158816 cyl, 16 head, 63 sec, 512 bytes/sect x 160086528 sectors
wd1: 32-bit data port
wd1: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 6 (Ultra/133)
wd0(piixide0:1:0): using PIO mode 4, Ultra-DMA mode 6 (Ultra/133) (using DMA)
wd1(piixide0:1:1): using PIO mode 4, Ultra-DMA mode 6 (Ultra/133) (using DMA)
boot device: wd0
root on wd0a dumps on wd0b
root file system type: ffs

--
Stephen