- log_sys.mutex was replaced with log_sys.latch as part of redo log revamp efforts.
- during the experiment it was observed that log_sys.latch spin-based variant
continue to perform better on ARM in the range of 8-15%.
(x86 didn't show any major performance difference).
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I think we might have more urgent problems, than that spinlock (for example, getting rid of lock-free transaction hash, the CPU for lf_finds is alarming). If it turns out to be hot, which it seems to be, I'm always for OS mutex, the pthread_mutex, or even for std::mutex, which for me turns out of to be native SRWLOCK. while does not seem to protect large section of code, I'm not sure how often it is entered, so it seems to be oft, and thus maybe we can stay with whatever is just normal mutex (if ARM likes spinning, there is this ADAPTIVE thing it may like). The mysql_mutex_t might give an idea of how hot it is, since it is perfschema-instrumented, on the other hand it might make it even hotter, exactly because of the perfschema overhead.