Other comments are querying the relevance of fsync() as a 'lag' benchmark, but I want to query whether fsync() is even meaningful at multiple calls per second.

Other comments are querying the relevance of fsync() as a 'lag' benchmark, but I want to query whether fsync() is even meaningful at multiple calls per second. I know fsync() ensures data gets written to disk, but why does anyone care that it can happen so often? When a device crashes, some data (prior to the sync) may be lost, but do we really need multiple checkpoints per second to ensure only sub-second data loss? I'd be content with a couple of minutes worth of loss even on my main PC, with its lack of battery backup. To enforce rapid syncs on a phone seems utterly pointless. Keep the syncs for meaningful checkpoints, like buying something in an app or marking a message as sent. Multiple fsync() calls per second are a total waste.