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The only asic that commit affects is r6xx chips. R7xx and newer are not affected since they use the async dma rings for bo moves and have since kernel 3.8 or so. The only time the new cpdma code would come into effect for newer chips is when you run the kernel bo tests. TBH, I don't know of any particular changes that would have had much impact on performance.
Alex, Michael mentioned some "a major ring handling clean-up" is it possible that the old 'dirty' code was inefficient and that the clean-up gave it a more direct, faster codepath ( or stopped hitting SLOW code paths). I could be totally wrong but if the blit work doesn't effect this test, thats the only other thing mentioned by Michael that stands out. Mesa 9.3 git also uses the SB backend by default, doesnt it? So does 3.12 include anything that a better shader compiler would benefit? Just spitballing idas here
Mesa 9.3 git also uses the SB backend by default, doesnt it?
It does now, yes. But (as I can see this as being a potential source of confusion), it should be noted that Michael has published earlier benchmarks utilizing 9.3 dev builds that came prior to the change which enabled sb by default.
Seeing as the results even surprised Alex, I'll run more tests today on a completely different system with various generations of AMD GPUs and try to get these results up tomorrow to see how those go.
Thanks, I and probably others here appreciate the time you put into Phoronix and am appreciative of you taking the time to run through this again. Not a lot of people would do something over like this, they'd probably publish it and call it quits.
3.12 does NOT turn DPM on by default. There were way too many changes in this kernel to consider the feature stable yet, but maybe 3.13 will do so. Also, the 4870 card michael is testing here is unlikely to get any performance benefit from it anyway - it's likely clocked high by default, and would just save power with DPM. It's the newer cards that tend to be clocked low by default and get big speedups - Radeon SI cards, Cayman, and the APU parts. And likely mobile as well.
OK, so these improvements are for other reasons. Even better!