Bill Davidsen wrote:
How about anything more? The truth is that much common hardware doesn't really make the cache to disk move visible, and turning off cache really hurts performance. And it would appear that fsync force a lot more data out of memory than just the blocks for the file in question.
Correct. That's the tradeoff with the ATA interface: you must be aware of the cache flush requirements when designing a solution such as a database that really cares about fsync(2), or a journalling filesystem.
However, the point I was making is that it would be useful to be able to tell when the write to non-volatile took place, not to force that to happen. Not to do anything which would flush a lot of other stuff and busy the drive. What I suggest is NOT fsync, just a way to assure ordering.
To make that possible, POSIX must become a transactional, async I/O API... :)
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