On 6/4/19 2:14 PM, Peter Zijlstra wrote: >> I worked on this owner merging patch mainly to alleviate the need to use >> cmpxchg for reader lock. cmpxchg_double() is certainly one possible >> solution though it won't work on older CPUs. We can have a config option >> to use cmpxchg_double as it may increase the size of other structures >> that embedded rwsem and impose additional alignment constraint. > cmpxchg8b was introduced with the Pentium (for PAE IIRC, it enabled > atomic 64bit PTEs, but Linux never used it for that) and every Intel/AMD > thereafter has had it. AFAIK there's no x86_64 chip without cmpxchg16b.
Thank for the clarification. I actually didn't check when cmpxch8b was introduced. I know it is a bit slower than regular cmpxchg. So we may still need to do some performance analysis to see how it compares with my current approach. Cheers, Longman
