On 26 May 2015 at 20:35, Avi Kivity wrote:
It can be important for O_DIRECT AIO operations. I agree that for buffered I/O, the filesystem overhead will dominate (and, on Linux, you don't have a way to implement futures over buffered I/O without resorting to threads, which will slow things down further).
Actually, on recent Linuces with ext4 reads from page cached data are now kaio wait free. It makes a big difference for warm cache filesystem when you're doing lots of small reads. Writes unfortunately still lock, and moreover exclude readers. Linux has a very long way to go to reach BSD and especially Windows for async i/o. Niall -- ned Productions Limited Consulting http://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/