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FOSDEM09: "Aggressive" Linux power managementFOSDEM09: "Aggressive" Linux power managementPosted Feb 12, 2009 16:10 UTC (Thu) by dlang (✭ supporter ✭, #313)In reply to: FOSDEM09: "Aggressive" Linux power management by johnkarp Parent article: FOSDEM09: "Aggressive" Linux power management
a couple of reasons.
1. even when the GPU has finished doing it's work you still want to see the screen (which requires that the GPU stay on)
2. changing the GPU mode can cause artifacts on the screen (mentioned in the article when talking about changing the clock speed)
3. switching modes takes time, you frequently don't want to drop too far as you then won't be able to respond to activity quickly. If you only switch modes when the entire system is idle, then you miss a lot of chances to save power.
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FOSDEM09: "Aggressive" Linux power management Posted Feb 12, 2009 16:24 UTC (Thu) by johnkarp (subscriber, #39285) [Link]
Re #1, isn't video memory typically dual-ported, so that the RAMDAC can still read the memory even while the GPU is inactive?
FOSDEM09: "Aggressive" Linux power management Posted Feb 12, 2009 16:41 UTC (Thu) by dlang (✭ supporter ✭, #313) [Link]
this will vary from video system to video system. some cards did use dual-port ram, but since some 'cards' can use your system ram, there are definantly 'cards' where that is not the case.
I don't know what's common on modern high-end cards
FOSDEM09: "Aggressive" Linux power management Posted Feb 13, 2009 8:30 UTC (Fri) by Los__D (guest, #15263) [Link]
I thought that cards using system RAM only used it for texture caches, and so on?
FOSDEM09: "Aggressive" Linux power management Posted Feb 19, 2009 22:26 UTC (Thu) by wmf (guest, #33791) [Link]
I think dual-ported VRAM was eliminated 5-10 years ago, and the RAMDAC has been part of the GPU for 10-15 years. It is probably possible to gate the command processor and shader pipelines while leaving the refresh logic on, though.
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