Originally posted by Volta
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Linus Torvalds Lands A 2.6% Performance Improvement With Minor Linux Kernel Patch
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Originally posted by kcrudup View PostIf i'm reading this right, this doesn't really help you if you run with "mitigations=off" right?
Speculation is just a feature of modern cpus, and needs to be dealt with at some points, but a barrier is the heaviest weight way deal with it. although I'm not a kernel guy and could be way off.
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Originally posted by fitzie View Post
Just because it mentions speculation doesn't mean that it's related to a mitigation. digging through the history of this code it seems like the adding the barrier to this function it seems like it was added to 6.11, because of something rust linux needed for googles effort to move binder to rust:
Speculation is just a feature of modern cpus, and needs to be dealt with at some points, but a barrier is the heaviest weight way deal with it. although I'm not a kernel guy and could be way off.
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Originally posted by marios View Post
I am not certain it is true. If Rust indeed causes 2.6% (at least) to C code though, even if it is for special cases, it is reason enough to kick it out of the kernel asap. Sadly it is not going to happen, because of the known reasons.
Enlighten us, o Nostradamus of Phoronix - what are these known reasons? And surely the lines with the same mitigation in the lib/usercopy.c were not related?
More seriously - Linux kernel code is messy. It's a wonderful piece of software, but the code quality in the kernel... highly varies, to say the least. Also, ultimately, all large software is bound to have some code smells and bugs. This is a mix of that, plus hardware issues with CPU speculation. See this post for seemingly the context of these changes: https://www.phoronix.com/news/Torval...rated-Buggy-HW
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