[Xen-devel] To use xcs or not?

[Jacob Gorm Hansen <jacobg@xxxxxxx>]

hi,

I am creating a graphics system where each VM draws into an OpenGL 
surface of a process running in dom0. I need to syncronize updates, 
ideally with the vertical blanking of the screen, but in the world of 
stupid PC hardware probably just with some refresh timer that my OpenGL 
process is tied to.
So when the screen has been redrawn, I need to wake up my domUs, and for 
this I wanted to use the ctrl_if mechanism. I borrowed some code from 
vm-shutdown in the (very nice) vm-tools package, setup a semaphore in 
the guest kernel, and for every screen update I send an XCS_REQUEST 
(only type that seems to do anything) up to the domU.
This works fine for a little while (1000 updates or so), whereafter xcs 
seems to go into an infinite loop. I am going to debug this a little, 
but before I dig in too dig I would like to know if this is the right 
solution for my problem. It seems a little worrying (performace wise) 
that all my notifications need to go via another user space process 
before reaching their destination. Would it be better to setup a 
dedicated event channel for this, and would doing so be possible from a 
user space process in dom0 (naturally I can create a special device node 
if I need to)?
Thanks,
Jacob


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