Perf regressions on many benchmarks with AMD Threadripper

[davidbolvansky]

Bugzilla Link	44411
Resolution	FIXED
Resolved on	Feb 25, 2020 07:55
Version	trunk
OS	Linux
Depends On	#43754 #43755 #43884
Blocks	#43900
CC	@alexey-bataev,@adibiagio,@topperc,@dwblaikie,@fhahn,@zmodem,@LebedevRI,@RKSimon,@rotateright,@yuanfang-chen

Extended Description

Phoronix ran some benchmarks with Clang 9/10 and GCC 9/10 on AMD. The article shows significant performance regressions in multiple benchmarks.

https://www.phoronix.com/scan.php?page=article&item=gcc-clang-3960x&num=2

[RKSimon]

This is unlikely to be AMD specific, at the very least it'll probably affect all Haswell-class (AVX2) CPUs - the article says as much:

"unfortunately the release build of LLVM Clang Git was pointing to performance regressions compared to LLVM Clang 9.0 stable. We've also seen Clang 10 running slower than Clang 9 on other systems and will have those additional results out in the coming days."

Is anyone setup with a suitable machine to run a git bisect script to track the regression(s) down?

[zmodem]

Sounds like the sub-bugs have been fixed or marked as wontfix. I'm guessing we're not looking further into this?

[davidbolvansky]

Right, it should be fine now

[adibiagio]

mentioned in issue #43884

[zmodem]

mentioned in issue #43900