[haiku-bugs] Re: [Haiku] #5383: MTRR regression: AGP transfer inconsistencies

  • From: "bonefish" <trac@xxxxxxxxxxxx>
  • Date: Thu, 18 Feb 2010 14:15:39 -0000

#5383: MTRR regression: AGP transfer inconsistencies
 Reporter:  rudolfc    |       Owner:  bonefish      
     Type:  bug        |      Status:  in-progress   
 Priority:  normal     |   Milestone:  R1            
Component:  - General  |     Version:  R1/Development
 Keywords:             |   Blockedby:                
 Platform:  All        |    Blocking:                
Changes (by bonefish):

  * blockedby:  5353 =>


 Replying to [comment:7 rudolfc]:
 > The driver's buffer is used for writing by the CPU only. The GPU reads
 from this buffer.
 > Using MTRR-WC has a big-time acceleration performance increase compared
 to write-trough or uncached (especially in accelerated 3D, I benchmarked
 this once).

 I was a bit surprised that WT is slower than WC, since the specification
 for WT says that "write-combining is allowed". Setting the frame buffer to
 WT instead of WC makes the graphics feel tremendously slower, so
 apparently the "is allowed" part doesn't mean it's actually done.

 Anyway, the problem should be fixed for P6 and later in r35515, since
 overlapping ranges are now handled correctly. Please close the ticket, if
 you can verify this.

Ticket URL: <http://dev.haiku-os.org/ticket/5383#comment:8>
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