On Sat, Apr 25, 2015 at 08:13:28PM +0200, Hannes Reinecke wrote: > I seem to remember having sent a similar patch about a year ago; This one? http://www.redhat.com/archives/dm-devel/2014-June/msg00023.html > which then got shot down due to the missing partial completion > handling. It got shot down because it passed the upper level request down, which is a non-no for blk-mq. > Anyway; we've discussed this at LSF in Boston, haven't we? > AFAICR we've found that having to resubmit the entire command > in the case of partial completion is okay with the storage > vendors, so this patch is a viable way of handling things. Yes. But even if it wasn't for some reason we could inspect blk_rq_bytes() on the clone and do a partial completion on the original request, but I'd prefer to avoid special casing this case if we can avoid it. > _But_ I really would like to have a consensus here that this > _is_ the correct way of handling partial request; because > if that is the case then we should adopt this strategy > throughout the SCSI layer (ie in scsi_io_completion()) > and document the fact. SCSI is a very different case, we do regularly get patial completions from arrays, and we need to handle them efficiently in the normal I/O path. The only case where we will resubmit completed I/O in dm-mpath is when we got a successfull partial completion in SCSI, and then a following completions returns an error that causes a failover. I don't think there is a need to micro-optimize this case. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
