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Re: [Xen-devel] VT is comically slow

On 3 Jul 2006, at 20:16, Rik van Riel wrote:

Are indications of IDE being used in PIO mode. Why this is, don't ask

A friend is trying out OpenBSD inside Xen, which shows more clearly
that HVM guests are indeed using PIO :(

pciide0 at pci0 dev 1 function 1 "Intel 82371SB IDE" rev 0x00: DMA, channel 0 wired to compatibility, channel 1 wired to compatibility
wd0 at pciide0 channel 0 drive 0: <QEMU HARDDISK>
wd0: 16-sector PIO, LBA, 20480MB, 41943040 sectors
wd0(pciide0:0:0): using PIO mode 2
pciide0: channel 1 disabled (no drives)

You might need to investigate ioemu/hw/ide.c to find out why Linux/*BSD are deciding to use PIO for data transfers. Intel put in considerable effort a while back to ensure that DMA was used. Maybe that's got broken.

 -- Keir

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