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SubjectRE: The GGI and EvStack debate -- Linus and such persons please reard.

On Fri, 27 Mar 1998, Jordan Mendelson wrote:

> Right now, graphics cards are one of the few devices which must be accessed
> directly from userspace with no kernel abstraction layer. How can anyone
> expect to run a real multi-user server when you have multiple programs
> trying to access video cards at once? While we are at it, why don't we pull
> the entire network card subsystem and put that into userspace too and see
> how long that survives in a real multi-user system. [...]

the problem is: video cards are 10 times more complex than networking
cards, they do 100 times more operations per second, and have 1/100th of
the latency. And, their perceived speed is 10 times more important to Joe
Average User.

unfortunately, kernel entry speed is constant, no matter what device you
use.

these 'small' _fundamental_ differences make GGI a _very_ _very_ _very_
delicate and sensitive hack, which has to be designed _very_ _very_
carefully. It's not a simple 'ah, why not put it into the kernel, it's a
hardware resource, isnt it?' decision. It might even be that it's not
possible to put it into the kernel, without accepting unacceptable
tradeoffs. Whats the problem with this, it's a _technical_ question. The
answer is yes or no, just _please_ dont try to answer that question
without thinking about the issue. [note that i'm not trying to answer the
question, i'm just trying to show you that it's not trivial to answer it
at all.]

and yes, _even_ networking drivers are being put into user-space to get
more speed and smaller latencies: take a look at Beowulf and U-Net ...

-- mingo


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