On Tue, 2002-10-22 at 21:13, Frank C. Earl wrote: > On Tuesday 22 October 2002 03:00 pm, you wrote: > > > But wouldnt it be nice to allow the graphics card to directly access > > the data from user space ? > > It seems to defeat the whole point of DMA, if you have to do multiple > > copies of the data. > > DMA allows you to do other things while the display chip's busy. DMA with > the RagePRO isn't safe (as in, can be reliably secured against malicious > clients using it to do exploits, etc...) so you have to audit the stream and > unmap the buffer (which will cause all kinds of cache miss pains per > Linus...) or copy the data across and DMA it from there. The copy method is > probably going to be faster than an audit and unmap because everything is in > cache with the copy operation.
Unmapping something, especially with threaded apps on SMP boxes is really really expensive. If you do the audit as you copy the data it may well actually cost no more than a single copy ------------------------------------------------------- This sf.net emial is sponsored by: Influence the future of Java(TM) technology. Join the Java Community Process(SM) (JCP(SM)) program now. http://ad.doubleclick.net/clk;4699841;7576301;v?http://www.sun.com/javavote _______________________________________________ Dri-devel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/dri-devel
