Developers split over split-lock detection

A "split lock" is a low-level memory-bus lock taken by the processor for a memory range that crosses a cache line. Most processors disallow split locks, but x86 implements them, Split locking may be convenient for developers, but it comes at a cost: a single split-locked instruction can occupy the memory bus for around 1,000 clock cycles. It is thus understandable that interest in eliminating split-lock operations is high. What is perhaps less understandable is that a patch set intended to detect split locks has been pending since (at least) May 2018, and it still is not poised to enter the mainline.

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