On Wed, Jun 11, 2025 at 11:11:28AM -0400, Chuck Lever wrote: > > If we're doing synchronous, direct I/O writes then why not just respond > > with FILE_SYNC? The write should be on the platter by the time it > > returns. > > Because "platter". On some devices, writes are slow. > > For some workloads, unstable is faster. I have an experimental series > that makes NFSD convert all NFS WRITEs to FILE_SYNC. It was not an > across the board win, even with an NVMe-backed file system. For everything that is not a pure overwrite on a file system that passes them through, and a device not having a volatile write cache FILE_SYNC currently is slower. That might change for file systems logging synchronous writes (I'm playing with that for XFS a bit again), but even then you only want to selectively do that when the client specifically requests O_DSYNC semantics as you'd easily overwhelm the log and introduce a log write amplification.
