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0 pointsasveikau4y ago0 comments

> Linux utilizes its Alpha port as a worst-case testbed for data race conditions in its kernel.

Is that still true in the present tense? Anybody doing this in 2021? Seems like alpha has been dead for a long time.

0 comments

Not Linux but the Linux formal memory model. The idea is that the compiler optimizations can be as nasty as the Alpha out of order execution engine and cache. The Linux code has to cater for these optimizations even though it will not result in an actual assembly instruction on anything except the Alpha. Problem is, on Alpha there's indeed an actual price to pay in performance for that nastiness.

asveikauOP4y ago

I suspect you misunderstand the question. My question is if anybody is presently using alpha hardware to verify such correctness. I understand memory models and barriers etc. and that alpha is one of the most relaxed on this front, that it historically influenced the kernel code and was previously very important test hardware. But the hardware is now very dated, to the point where it might not be good test hardware.

bonzini4y ago

The answer to that question is no, but the Alpha is still considered the least common denominator even though the hardware is obsolete. When people write litmus tests for the Linux memory model they are still validated against Alpha semantics, because compiler optimizations have the same reordering effects as the weird caches of Alpha processors.

(The stroke of genius of the C++11 memory model, compared to the older Java memory model, was that reordering could be treated the same way no matter if performed by processors or compilers).

mhh__4y ago

I know that GCC for example is tested on a bunch of wacky old - read: obsolete ;) - hardware, so it's certainly possible that the same is true for Linux.

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bonzini4y ago

asveikauOP4y ago

bonzini4y ago

(The stroke of genius of the C++11 memory model, compared to the older Java memory model, was that reordering could be treated the same way no matter if performed by processors or compilers).

mhh__4y ago

I know that GCC for example is tested on a bunch of wacky old - read: obsolete ;) - hardware, so it's certainly possible that the same is true for Linux.

j / k navigate · click thread line to collapse