By Luck, Marek Discovers A "Serious Performance Fix" For RadeonSI

[phoronix]

Phoronix: By Luck, Marek Discovers A "Serious Performance Fix" For RadeonSI

Marek Olšák, the prolific longtime contributor to Mesa and AMD developer, published a patch today with a big performance improvement that he says has been discovered by luck...

http://www.phoronix.com/scan.php?page=news_item&px=RadeonSI-Lucky-ReZ-Fix

[bibaheu]

Thanks Marek, good job! My 290x will remember your name when it finally burns to ashes for pushing so many frames

[AdamOne]

Oooohhh snap!

[M@yeulC]

Sweet!

I wonder if there is some other hidden gems like this one. There might be one or to, but I would expect the probability to be quite low.
Thanks a lot, Marek!

I would be curious to know if it was 100% by accident, or a performance investigation was under way?

[ElectricPrism]

Thank you Marek, thank you all MESA developers

I bet on you guys when I switched to red camp 2 months ago and you guys really are doing a pro job making MESA super awesome. Great work, looking forward to more optimizations and awesomeness.

[oxwivi]

So what is that thing being disabled? Why does it reduce performance? It was added for a reason.

[LinAGKar]

How does this affect other games?

[smitty3268]

So what is that thing being disabled? Why does it reduce performance? It was added for a reason.

It's part of the HiZ optimizations the hardware can do to cull out parts of the scene that can't be viewed. Different optimizations are enabled in the hardware for different cases.

The original commit notes: This can increase perf for shaders that kill pixels (kill, alpha-test, alpha-to-coverage).

The new commits seem to indicate that it can still be faster in some cases, but without profiling it should be assumed to be slower. Therefore, they've just disabled it by default for now, until/unless they can figure out what kind of heuristic to use to enable it.

How does this affect other games?

There's another bug report from February that says it should speed up Unigine Valley by 20%. It was only enabled on certain expensive shaders to begin with, so expect no change to light apps such as OpenArena.

[treba]

Wow with all these little fixes and performance improvemento (and of course with ogl 4.4/4.5 enabled on radeonsi), mesa 13 will be a great enhancement. Hope the intel shader caches land before friday and fedora 25 picks it up!

[AndyChow]

It's not really by luck. The guy is an expert and top-notch programmer. He created this improvement by being an expert and trying things.