Re: [Xen-devel] xen-unstable qemu-upstream: pci-passthrough timing issues due to commit 0f7b2864d0d0c3ef2801f9214d8c510c80a220d1 when vnc enabled

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

Monday, April 22, 2013, 12:01:02 PM, you wrote:

> On Sat, 20 Apr 2013, Sander Eikelenboom wrote:
>> Hi Gerd,
>> 
>> Using qemu-upstream with pci-passthrough on xen-unstable previously worked 
>> fine.
>> Since commit 0f7b2864d0d0c3ef2801f9214d8c510c80a220d1 (bisected) i see what 
>> i think are timing issues (video device is reporting buffer underruns).
>> 
>> Since that commit changes vnc code, i have disabled vnc (was default 
>> enabled, but i did not use it).
>> Disabling vnc by using vnc=0 and nographic make thinks work like before.

> Are you sure that the bug is related to Xen PCI passthrough (it doesn't
> happen if you don't assign any devices to the Xen guest)?
> I am asking because the Xen PCI passthrough code doesn't use any timers,
> while this looks like something related to timer and refresh
> intervals...


Ok latency issue would perhaps be a better description.
I think something in this change make it worse, hence resulting in the driver 
of the passthroughed pci device reporting that it's buffer was empty (4 times) 
and then the buffer is filled up with 4 frames where it expected only 1.

Anyhow i noticed that running with "nographic" dramatically reduces the 
overhead of the qemu process in dom0 compared to running with graphics.
Which seems strange since it's a console only linux guest and no vnc clients 
are connected ...

--
Sander


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