[Xen-users] Issues with PCI Passthrough and domU Memory Amount

["Nick Couchman" <Nick.Couchman@xxxxxxxxx>]

Hey, Everyone,
I know I've asked about this, before, but I'm hoping that someone has
some new insight into this problem.  I'm using Xen 4.0.0 and 4.0.1 on
Dell Optiplex 780 machines.  I'm running Xen with an OpenSuSE
11.2/11.3/11.4 install, a Windows domU, and am passing through graphics,
USB, and audio PCI devices from the host machine to the Windows domU.
In general, this works pretty well, but I've hit upon an issue that
seems pretty consistent across the versions of Xen and Linux dom0s.
Basically, the more I increase the amount of RAM assigned to the Windows
domU, the longer the domU takes to start (not the O/S to boot, just Xen
to get the domU running and dom0 to hand over all the resources).  So,
with 2GB of RAM assigned to the domU, it starts reasonably quickly and
proceeds to boot Windows.  With 2.5GB, the boot time is longer, but
still short enough to actually get it going (takes 2-3 minutes between
executing the "xm start <domu>" command and when I see the domU BIOS
screen).  Once I hit 3GB, it takes so long between the start command
when the domU can actually get going, that one of the Xen timeouts is
reached and Xen fails to start the domU.

Anyone have any insight into this?  Log files don't seem to indicate a
lot - in fact, the qemu-dm log files spit out exactly the same thing for
the successful start and the unsuccessful start.  I'd appreciate any
ideas to try to reduce the amount of time or to at least figure out why
it takes Xen and/or dom0 so long to get these domUs up and running.

Thanks,
Nick



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