[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [RFC] PVFB: Add refresh period to XenStore parameters?
Markus Armbruster, le Tue 04 Mar 2008 16:48:20 +0100, a écrit : > Samuel Thibault <samuel.thibault@xxxxxxxxxxxxx> writes: > > Markus Armbruster, le Tue 04 Mar 2008 15:32:57 +0100, a écrit : > >> > In my case, I'm using PVFB to expose the stubdomain qemu display. The > >> > problem is that every 30ms, qemu wakes up to memcmp() the whole video > >> > memory with a shadow buffer so as to track changes. If it knew that the > >> > >> Wait a second! You're talking about *your* frontend here, aren't you? > >> > >> Maintaining a shadow copy in the frontend (which requires compare and > >> copy) to minimize copying in the backend sounds pretty self-defeating > >> to me. Why is this a good idea? > > > > Because in my case the domain is HVM, and I don't want to trap the > > writes to the video RAM since that's awfully slow. > > > >> Why not refrain from sending update messages and have the backend > >> simply redisplay everything? > > > > Because as explained above, I can't avoid a shadow copy. > > I imagine (perhaps naively): > > * The domU writes to a framebuffer provided by the frontend. > > * The framebuffer (not a copy of it) can be shared with the backend, > which only reads. Well, that's not always the case, when the guest is in text mode for instance, the PV shared buffer is converted from the guest text buffer. > * If the frontend can track changes efficiently, it sends update > messages to the backend, which can use them to only redisplay > changed areas. > > Else the backend needs to assume the worst and periodically > redisplay everything. It is free to maintain a shadow copy to track > changes and minimize redisplay, if that turns out to be faster. > > What's wrong with that? Well, that was actually my next target :) (but for that we badly need the resize/redepth support). However, that doesn't solve something that still bugs me, which is that the VGA emulation layer wakes up every 30ms to just notice that the width/height/depth registers didn't change etc. even if the actual window is not shown. Samuel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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