On Tue, Jun 11, 2013 at 01:41:38PM +0200, Hannes Reinecke wrote: > I currently playing around with improving SCSI EH, optimizing > command aborts and the like. > > And, supposing it to be a nice testbed, tried to make things work > with virtio_scsi. > > However, looking at the code there I've found virtscsi_tmf() just > uses 'wait_for_completion', with no timeout specified. So in effect > any abort might stall forever. > > Wouldn't it be more sensible to use 'wait_for_completion_timeout' > here, to allow the error escalation to continue? > This would especially be useful when running with multipathing, > as the underlying device might stall, and aio_cancel() doesn't work > reliably, if at all.
Hi, I agree that we need a timeout. bdrv_aio_cancel() is not guaranteed to complete in bounded time. > Also I've found that there is no host reset. Currently the virtio > semantics seem to require reliable communication, ie for every > command send there _has_ to be a response. > > Long and painful experience with RAID HBAs has shown that this model > works okay for the lower-level escalations, but you absolutely need > a host reset to restore communication. > In the case of virtio I would think that a virtio-level reset for > host_reset would be a sensible idea. One thing to watch out for is that a virtio-scsi reset will likely hang too because it resets all pending requests. Paolo Bonzini has done the lion's share of virtio-scsi work over the past year (or two?). He might have some more thoughts. Stefan
