Re: Re: how to write snappy benchmark?

On Sun, Jul 06, 2003 at 08:19:26PM -0400, Havoc Pennington wrote:
> Not sure backing store papers over the real problem. Two real problems
> it's the correct solution for are:
> 
>  - expose event -> application -> repaint round trip causes latency;
>    saving window contents on the server side is the right solution 
>    here, it avoids the round trip entirely

If this is your reason for backing store for apps running locally,
then it is papering over the real problem. If local apps can't
complete the above loop very quickly, then there is a real problem
that is going to negatively affect interactivity elsewhere.

I could see an argument for considering backing store an automatic
server-side operation for windows running on a remote machine.
 
>  - recomputing what to render is expensive. For example, drawing
>    Unicode text involves a fair bit of glyph selection, positioning,
>    and so forth. The best way to cache that may well be in pixmap
>    form, i.e. by just saving the pixels that were drawn, rather 
>    than caching it at any higher level.

This certainly makes sense on a per-application basis. This is exactly
what happens in pretty much every environment out there. If you want
to backing store your windows, go ahead. It would probably make sense
to make it easy within GTK+ and other toolkits to "check a box" and
have a window backing stored on the server instead of the
client. However, this isn't the general case solution to improve
display response time.

> If the bottleneck is either of those things (and it may well be,
> though we still have no hard profile data), then backing store isn't a
> band-aid, it's exactly the right fix and it does solve the problem.

Doing backing store to fix the event latency problem generates a
system which feels just like OS X. It's "solid and correct" but it's
piggish. Users don't want piggish, we want rippin fast like
Windows. Users just put up with piggish when they have to.

-- 
David Jeske (N9LCA) + http://www.chat.net/~jeske/ + [email protected]