On Tue, Apr 04, 2023 at 04:51:08PM -0700, Dan Williams wrote: > Gregory Price wrote: > [..] > > More generally, I think a cxl-swap (cswap? ;V) would be useful exactly to > > help identify when watch-and-wait tiering becomes more performant than > > promote-on-first-use. If you can't beat a simple fast-swap, why bother? > > I think it is instructive to look at what happened with PMEM, i.e. a > "pswap" idea never entered the discourse. The moment the memory is not > byte-addressable, it might as well be an NVME device where it can > support a queue-depth and async-dma. touché, but then did pmem hit latencies as high as 1.5-2us? (I honestly don't know). I'm just wondering how useful a 2mb page of memory at 1.5us per fetch is, and whether we'll find it's almost always beneficial to promote that page one first/second/third cache line fetch in some interval. If you always promote on first use, it's basically just super-swap - even if the memory is still itself still byte-addressable.
