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No you don't have to fsync. Think of it like RAM. You don't fsync RAM.

You do, in fact. It’s called a memory write barrier. Ensures consistency of data structures as needed. And it call stall the cpu pipeline, so there’s a nontrivial cost involved.

The point is that on PMem that is simply "sfence", and not a potentially super-expensive "fsync" syscall... Fsync is an fsync, not a memory barrier...

They both involve flushing cache to backing stores, and waiting for confirmation of the write. It’s literally the same thing. It’s just writing a cache line to RAM is orders of magnitude faster than writing a disk sector to storage, even with NVME SSDs. Octane is/was somewhere in the middle.

> They both involve flushing cache to backing stores, and waiting for confirmation of the write.

No they don't. A fence only imposes ordering. It's instant. It can increase the chance of a stall when it forbids certain optimizations, but it won't cause a stall by itself.

CLWB is a small flush, but as tanelpoder explained the more recent CPUs did not need CLWB.

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