On Sunday, January 25, 2009 2:28 am Pekka Paalanen wrote: > On Mon, 5 Jan 2009 18:55:50 -0200 > > Tiago Vignatti <vigna...@c3sl.ufpr.br> wrote: > > Hi guys, > > > > Under KMS, we can build a feature to update the cursor directly to screen > > without the continuous intervention of the userspace application (X > > server, wayland, etc). It's a fastpath for DRM based cursors obtained by > > short-circuit the kernel input layer and DRM module. This would solve all > > cursor's latency issues that we have in our current model [0]. > > Reducing latency is a good idea, but I don't think circumventing user space > altogether is so good. Consider a case where user space is stalled due to > excessive load, and let's think about usability. Much of usability comes > from feedback given to a user. > > If cursor updates are done completely inside the kernel, the mouse will > continue to work without any hiccups under severe load (this is what you > are aiming for, right?). The user clicks a button, and nothing happens in > the GUI, since user space is stalled. The user clicks again. And again. > Then clicks another button. It takes several seconds for the user to > realize, that the clicks are not getting processed. What's worse, all the > clicks are probably queued now and will be processed later, possibly > leading to unexpected results. > > If cursor updates had to visit user space, the mouse cursor would stall > and jump. This is bad behaviour in itself, but it is also an immediate > feedback to the user, that the system is not responsive. The user cannot > even reach a button to click it, before he sees that something is going on. > In a bad situation, I think this is the less evil choice.
SGI did some use case studies on this. The conclusion they drew was that the cursor should *always* be responsive, and so that's what they did back in the old days on IRIX. Unfortunately we don't have access to that data so we don't know the circumstances under which they tested users, or what the tradeoffs were. But personally I think it sucks when the pointer jumps around, no matter what the situation is with the machine. It makes the whole OS seem cheap and crappy. And for a more "typical" user, I still think smooth movement makes sense. We already have other ways of communicating "system/program busy" than cursor movement (greyed out windows for instance), so I don't buy that argument either. -- Jesse Barnes, Intel Open Source Technology Center ------------------------------------------------------------------------------ This SF.net email is sponsored by: SourcForge Community SourceForge wants to tell your story. http://p.sf.net/sfu/sf-spreadtheword -- _______________________________________________ Dri-devel mailing list Dri-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/dri-devel