Re: [Xen-users] Spectacularly disappointing disk throughput

[Florian Heigl <florian.heigl@xxxxxxxxx>]

Hi Chris,

unfortunately, thats over my head.
I think you're correct that the PV drivers cannot possible handle a
PCI passthrough device.

With the FreeBSD domU I had built I also had to switch the device type
in the Xen config, albeit that was still on Xen 4.0.
I can't read through your notes, just not enough time. But it can't
hurt to check the backend for your PV disks is also really "blkback".
Me thinks. On the other hand I'm not 100% sure this would be still
true on PVOPS host kernels.


I havent been back to using PCI delegation since a few years ago;
Adaptec SCSI controllers and their irq sharing flaws made my host
crash and I was simply fed up with it.
First thing to check with bad SATA performance on your passthroughed
controller would be if the AHCI disk access works.
I hope you delegated the full controller and not a single pci function
of the controller? that would make me worry.

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.

Florian

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