Il 25/11/2013 14:57, Peter Lieven ha scritto:
> + /* Guess the internal cluster (page) size of the iscsi target by the
> means
> + * of opt_unmap_gran. Transfer the unmap granularity only if it has a
> + * reasonable size for bdi->cluster_size */
> + if (iscsilun->bl.opt_unmap_gran * iscsilun->block_size >= 64 * 1024 &&
> + iscsilun->bl.opt_unmap_gran * iscsilun->block_size <= 16 * 1024 *
> 1024) {
> + bdi->cluster_size = iscsilun->bl.opt_unmap_gran *
> iscsilun->block_size;
> + }
I think you are mixing many different concepts:
* The optimal unmap granularity is good as a suggestion for the cluster
size of higher-level formats.
* The optimal transfer granularity (block limits page, bytes 6-7,
min_io_size in Linux) could be used to adjust the length of transfers in
"qemu-img convert". I have not really thought much about *how* to do it.
* The optimal transfer (block limits page, bytes 12-15, opt_io_size in
Linux) should not be used in "qemu-img convert", I think, unless you can
actually report performance improvements. This is because in "qemu-img
convert" we need to write the data anyway to the target. We cannot
schedule other commands between two transfers. So I don't think any
delays incurred by a very large write should matter.
The maximum transfer length (block limits page, bytes 8-11) should be
handled instead in the iSCSI driver, but I do not see the need to do
this unless we have reports of something not working.
Paolo
