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[Xen-devel] xhci passthrough

To: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] xhci passthrough
From: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
Date: Thu, 28 Oct 2010 00:01:18 +0200
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Hi Konrad,

Due to a 2.6.37-merge-window kernel now being able to boot under Xen i was able 
to test my xhci controller under dom0 which i previously couldn't.

The results:
A) 2.6.37-merge-window kernel baremetal: Videograbbing while doing 20 
iterations of make -j6 of kernel works.
B) Xen + 2.6.37-merge-window kernel as Dom0: Videograbbing while doing 20 
iterations of make -j6 of kernel works.
C) Xen + pvops dom0 +  2.6.37-merge-window kernel DomU: Videograbbing 
while doing 20 iterations of make -j6  still freezes the machine without a 
trace after a short while.

An other interesting thing is the interrupt rate i see in /proc/interrrupts for 
the xhci controller, i measured for 5 minutes each time.
In situation:
A) About 3200 Interrupts/second
B) About 3200 Interrupts/second
C) About 7800 Interrupts/second, what would be 7.8 interrupt per ms which seems 
to work as long as you don't stress the rest to the limit.
   Which probably causes some sort of deadlock (some where in the path from 
device, xen, dom0/pciback , domU/pcifront, xhci driver, application.) when not 
delivered on time or when it boldly goes on a code path where no one has gone 
before ..

Compared with a measurement of interrupts by a USB2 controller:
Around 155 Interrupts/second

Probably a silly question without a right answer ... but what interrupt rate 
would you guess it should be able to take ?
And is it logically that when passed through it causes around 2.5 times more 
interrupts ?

Now testing on a Intel(R) Core(TM)2 Quad CPU    Q9400  @ 2.66GHz



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