On Fri, Dec 25, 2009 at 08:22:38AM -0800, Larry McVoy wrote: > > Dudes, sync() doesn't flush the fs cache, you have to unmount for that. > Once upon a time Linux had an ioctl() to flush the fs buffers, I used > it in lmbench. > > ioctl(fd, BLKFLSBUF, 0); > > No idea if that is still supported, but sync() is a joke for benchmarking. Depends on what you are trying to do (flush has multiple meanings, so using can be ambiguous). BLKFLSBUF will write out any dirty buffers, *and* empty the buffer cache. I use it when benchmarking e2fsck optimization. It doesn't do anything for the page cache. If you are measuring the time to write a file, using fsync() or sync() will include the time to actually write the data to disk. It won't empty caches, though; if you are going to measure read as well as writes, then you'll probably want to do something like "echo 3 > /proc/sys/vm/drop-caches". - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
