Am 27.07.2011 21:57, schrieb Christoph Hellwig: > On Wed, Jul 27, 2011 at 09:52:51PM +0200, Frediano Ziglio wrote: >> Also I notice that combining XFS, Linux AIO, O_DIRECT and O_DSYNC give >> impressive performance but currently there is no way to specify all that >> flags together cause nocache enable O_DIRECT while O_DSYNC is enabled with >> writethrough. > > Indeed. This has come up a few times, and actually is a mostly trivial > task. Maybe we should give up waiting for -blockdev and separate cache > mode settings and allow a nocache-writethrough or similar mode now? It's > going to be around 10 lines of code + documentation.
I understand that there may be reasons for using O_DIRECT | O_DSYNC, but what is the explanation for O_DSYNC improving performance? Christoph, on another note: Can we rely on Linux AIO never returning short writes except on EOF? Currently we return -EINVAL in this case, so I hope it's true or we wouldn't return the correct error code. The reason why I'm asking is because I want to allow reads across EOF for growable images and pad with zeros (the synchronous code does this today in order to allow bdrv_pread/pwrite to work, and when we start using coroutines in the block layer, these cases will hit the AIO paths). Kevin
