Re: accel handling

[Marcus Sundberg <erammsu@kieraypc01.p.y.ki.era.ericsson.se>]

Vladimir Dergachev wrote:
> 
> On Mon, 30 Aug 1999, Stephen C. Tweedie wrote:
> 
> > Hi,
> > The only way to do it is to flip page tables while the accel engine is
> > running.  You may want to restore it on demand by trapping the page
> > fault on the framebuffer and stalling until the accel lock is released.
> > This can be done, but it is really expensive: you are doing a whole pile
> > of messy VM operations every time you want to trigger the accel engine
> > (any idea how often you want to flip the protection, btw?)
[snip]
> What about forbidding concurrency for the processes that have mmapped
> the framebuffer/accelerator ? Say assign all of them to one(or same) cpu
> permanently.

Not an acceptable solution. You may have several threads clone()d off
after the framebuffer have been mapped, and they may not do anything
related to graphics.

But by only re-mapping the framebuffer on demand as Stephen said you
can avoid repeatedly un-mapping the framebuffer for processes/threads
that doesn't use it.

//Marcus
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        Marcus Sundberg        | http://www.stacken.kth.se/~mackan/
 Royal Institute of Technology |       Phone: +46 707 295404
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