On Thu, 2017-03-09 at 02:53 -0600, Mike Christie wrote: > On 03/08/2017 10:22 PM, Nicholas A. Bellinger wrote: > > On Wed, 2017-03-08 at 20:16 -0800, Nicholas A. Bellinger wrote: > >> On Wed, 2017-03-08 at 12:02 -0600, Mike Christie wrote: > > > > <SNIP> > > > >>> > >>> My tcmu-runner plan was: > >>> > >>> 1. For hung commands, we are going to add callouts to the backend module > >>> for TMFs. target_core_tmr.c would call them during TMFs like ABORT_TASK > >>> to have the backend perform the TMF. target_core_user would then call > >>> into tcmu-runner and that would call into the userspace handler. > >>> > >> > >> Mmmm. This would mean TMRs would function very different between TCMU > >> and non TCMU backends.. > > Do we ever want support for that? I actually started implementing > support so lio backends like iblock could call into the initiator > driver's error handlers: > > http://www.spinics.net/lists/linux-scsi/msg97064.html > Propagating target LUN_RESETs into LLD driver code, specifically in cases where the LLD has a higher host reset timeout would certainly be useful to reduce the overall end-to-end host-reset recovery time. That said, I don't think the various pros/cons of this approach have ever been verbalized on the list, so I'd like to give it some more thought to understand what the downsides (if any) are. > For tcmu, your idea below works nicely. I will work on it. Thanks. > Ok, I'll post an updated patch to make target_complete_cmd() handle SAM_STAT_BUSY + SAM_STAT_QUEUE_FULL as a v4.12 item. > >> > >> We've always had the assumption that once a TMR is processed, code > >> blocks until the backend completes outstanding se_cmd(s) in question > >> without an explicit cancellation trigger. > >> > >> One approach I've taken for a out-of-tree make_request_fn() based bio > >> driver is return bios with -EAGAIN if a bio takes more than say 3 > >> seconds to complete, in order to signal to IBLOCK to propagate up a > >> SAM_STAT_BUSY or SAM_STAT_QUEUE_FULL. This ends up working quite well > >> to keep initiators happy, and virtually eliminates spurious TMRs in host > >> environments (like ESX for example) with a very low SCSI timeout. > >> > >> Of course, this pushes alot of smarts into the driver below the backend, > >> but in a distributed scale out backend where I/Os delays, et al. are a > >> fact of life this is difficult to avoid. > >> > >> So that said, I'd prefer to have TCMU's user-space code return back I/Os > >> that are expected to take a long time with SAM_STAT_BUSY or > >> SAM_STAT_QUEUE_FULL (to reduce host queue_depth), instead of adding a > >> explicit se_cmd cancellation mechanism in target-core into backend > >> driver code. > >> > >> I'd be happy to post the target-core changes needed to do this, which > >> where posted at one point but ended up not getting merged. > > > > Btw, here is the patch in question: > > > > http://www.spinics.net/lists/target-devel/msg11835.html > > > -- > To unsubscribe from this list: send the line "unsubscribe target-devel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe target-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
