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[Xen-devel] [PATCH 0/3] Enhance VNC mouse/video handling

The following 3 patches enhance the VMX device model by adding the
following features:

1)  Add Summagraphics Tablet emulation for VNC users.  The current
PS/2 emulation is unusable under VNC since PS/2 provides mouse deltas while 
VNC only provides absolute coordinates.  Note that the guest must be
configured properly, for example the `gpm' demon should be started with 
the command:

        gpm -t summa -m /dev/ttyS0

and the X-Windows mouse stanza should look something like:

    Section "InputDevice"
        Identifier   "Summa Mouse"
        Driver       "summa"
        Option       "CorePointer"
        Option       "Device"             "/dev/ttyS0"
        Option       "Protocol"           "Auto"
        Option       "InputFashion"       "Tablet"
        Option       "Mode"               "Absolute"
        Option       "Compatible"         "True"
        Option       "SendCoreEvents"     "on"
        Option       "Vendor"             "GENIUS"

Also note that the Summagraphics emulation will NOT work when using
SDL, make sure your guest is configured for a PS/2 mouse if you are
using SDL. 

2)  Change the VNC main input loop delay from 1 second down to 10
msec.  The 1 second delay was causing significant latency problems
with the mouse while there is no measurable overhead in lowering the
delay down to 10 msec. 

3)  Add a shadow VRAM to track changes to the real VRAM.  When the guest 
OS was given write access to the VRAM the device model tracked all
VRAM changes by updating the entire screen on every output loop,
causing significant overhead (a CPU bound loop in a guest slows down
by about 35%) and significant mouse latency (VNC uses the same data
path for mouse events and video updates).  With the shadow VRAM only
modified pages need to be updated and the comparison of the shadow
VRAM to the real VRAM only adds ~4% overhead while eliminating the
mouse latencies. 

Don Dugger
"Censeo Toto nos in Kansa esse decisse." - D. Gale
Ph: (303)440-1368

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