To XCB or not to XCB ...

[Jamey Sharp]

On Sat, Aug 26, 2006 at 10:07:26AM -0700, Kean Johnston wrote:
> One other question. For creating a new distribution what is the
> conventional wisdom about XCB? If I dont include it, will it
> cripple X in any way? If I do, will there be any performance
> benefits or deficits? The web page wasn't very enlightening,
> so if someone can put forth an educated opinion, I would
> greatly appreciate it. Thanks.

We haven't formally released XCB yet (mostly we just need release
engineering at this point), and the version of Xlib built with XCB
should be more widely tested before declaring it stable. However, I know
of no correctness bugs in either.

There is a very small, but measurable, performance hit to using XCB,
made marginally worse when Xlib is used on top. We know how to improve
this performance somewhat, but it hasn't happened yet. Of course, when
apps and libraries start migrating to XCB, they'll be able to gain
significant performance improvements by taking advantage of XCB's better
API.

I've been running essentially the current version of Xlib/XCB on my
laptop in lieu of stock Xlib since early this year, up to fixing a
couple of bugs in that time, and I don't believe there is any
perceptible performance difference on real applications, nor have I
encountered any bugs in months. I've been testing out a bunch of new X
apps recently, too. :-)

In summary: we need to get a release out of both XCB and Xlib/XCB, RSN,
and vendors probably shouldn't ship the XCB stack until we do. But if
you have an 'experimental' repository to distribute it in or want to
test it yourself, I'd strongly encourage that.

Hope that helps: thanks for asking!

--Jamey
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