Re: Re: how to write snappy benchmark?

On Mon, Jul 07, 2003 at 11:14:34AM -0700, Mark Vojkovich wrote:
| > 
| > |    I believe that direct rendering will make the latency worse in
| > | the case of exposures.  It does for 3D.  Nothing has changed from
| > | the description I gave above except that now the apps all have
| > | to synchronize with the X-server before they can render.  ...
| > 
| > That wasn't true for systems I've worked on in the past, so I don't
| > believe it's true in general.  If it's a bottleneck in our current
| > systems, at least it's something those of us working at the low level
| > can fix to make life easier for those higher in the food chain.
| > 
|    Perhaps you can give a specific platform and an example of 
| how moving a window while 3D is running doesn't insert pipeline
| bubbles.

First you said that the apps have to synchronize with the X server.  Now
you say that a pipeline bubble has to be introduced.  Those aren't at
all the same thing, so be careful about which claim you're really trying
to make.

On systems where the command stream to the drawing engine uses
window-relative coordinates and doesn't include any information derived
from the clipping region, the X server pauses the command stream from
the app, adjusts window-origin and clipping information, then restarts
the command stream.  This usually does introduce bubbles (in-flight
drawing operations have to drain from the pipe), but there's no
handshake between the app and the server.  In particular there's no
round-trip communication between the two.  

So I'll stick by my original assertion that synchronization isn't
required, and if the synchronization that's happening with today's
systems is causing a problem, then it's something those of us working on
low-level graphics should try to improve.  Don't try to read any more
into it than that.

Allen