EXA and MigrationHeuristic

[Maarten Maathuis]

On Fri, May 30, 2008 at 9:45 AM, Michel Dänzer
<michel at tungstengraphics.com> wrote:
> 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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Maybe it's an idea to change the migration default for drivers that
only provide blit and and solid fill, in any other case always is the
right default (imo).

Maarten.