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Re: [Xen-users] Spectacularly disappointing disk throughput

Hi Florian,

> First thing to check with bad SATA performance on your passthroughed
> controller would be if the AHCI disk access works.

Interesting point. My first citation at the beginning of this thread
referenced disk devices at /dev/adaX. I believe that this means AHCI
is working.

...But they're now /at /dev/adX, so AHCI is not working currently. It
doesn't seem to make any difference, because the performance numbers
are identical.

I've since added 'device ahci' to my kernel configuration and am
building a new kernel right now. I hope to get ahci working again.

> I hope you delegated the full controller and not a single pci function
> of the controller? that would make me worry.

I belive so. I've delegated '00:11.0'. I think that '.0' is the
function? It's the only one on '00:11'

# lspci -s 00:11
00:11.0 SATA controller: ATI Technologies Inc SB700/SB800 SATA
Controller [AHCI mode] (rev 40)

> It would be good if you could test the passthrough SATA performance in
> a HVM linux or windows domU to get some more data about this.
> But if I had only one shot: AHCI not working.

I tried to boot the debian squeeze installer as an HVM, but it kept
coming up in PV mode, so I grabbed a Lenny installation image, and
booted it like this:

name = 'lenny-installer'
kernel = "/usr/lib/xen-4.0/boot/hvmloader"
builder = 'hvm'
memory = 1024
device_model = '/usr/lib/xen-4.0/bin/qemu-dm'
disk = [ 'phy:/dev/loop1,ioemu:hdb:cdrom,r', ]
pci = [ '00:11.0' ]

I'm pretty confident that it's an HVM because:
# xm list -l lenny-installer | grep -A 1 image

This guest is able to read from the SATA drives in excess of 100MB/s,
while FreeBSD gives less than 0.5MB/s :(

Does the test look like it is sound?

Thanks again.


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