EXA and MigrationHeuristic

Michel Dänzer michel at tungstengraphics.com
Fri May 30 00:45:52 PDT 2008

On Thu, 2008-05-29 at 14:01 +0200, Juliusz Chroboczek wrote: 
> > "greedy" is faster than "always" in some cases because it's quite
> > conservative about migrating pixmaps offscreen. Any single low level
> > operation can only be accelerated if all pixmaps involved are offscreen,
> > so this results in fewer operations being accelerated, thereby avoiding
> > migration overhead for operations that can't be accelerated for other
> > reasons.
> Let me change the emphasis.  Main-memory pixmaps are moderately fast
> for all operations.  Off-screen pixmaps are very fast for some
> operations, and glacially slow for others.

No, that's not how it is or what I said. Anyway, I'll leave the flaming
fun to you guys in my western neighbour country. ;)

That said, while I think changing the default would clearly be a bad
idea for the Git master branch, for stable branches and distros it's
ultimately up to the respective maintainers of course. However, I think
the decision should be based on more than some specific use cases that
don't represent what EXA is designed to do well.

Also, from the Ubuntu log snippet somebody pasted, it looks like their
change might even prevent using the other heuristics at all, which would
be very bad. Even if that's not the case, it might have been nice to
discuss it with upstream beforehand.

Earthling Michel Dänzer           |          http://tungstengraphics.com
Libre software enthusiast         |          Debian, X and DRI developer

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