On 06/10/2013 10:20 AM, Christoph Hellwig wrote: > On Mon, Jun 10, 2013 at 09:40:52AM +0200, Hannes Reinecke wrote: >> When a command runs into a timeout we need to send an 'ABORT TASK' >> TMF. This is typically done by the 'eh_abort_handler' LLDD callback. >> >> Conceptually, however, this function is a normal SCSI command, so >> there is no need to enter the error handler. >> >> This patch implements a new scsi_abort_command() function which >> invokes an asynchronous function scsi_eh_abort_handler() to >> abort the commands via 'eh_abort_handler'. >> >> If the 'eh_abort_handler' returns SUCCESS or FAST_IO_FAIL the >> command will be retried if possible. If no retries are allowed >> the command will be returned immediately, as we have to assume >> the TMF succeeded and the command is completed with the LLDD. >> If the TMF fails the command will be pushed back onto the >> list of failed commands and the SCSI EH handler will be >> called immediately for all timed-out commands. > > Why can't we use a work item per command? Linking things into a list > just to queue it up to workqueues missed half of the point of the > workqueue infrastructure. > Hmm. I felt that using a per command workqueue might be a bit excessive. Also the current semantics call for a synchronous command abort. So even using a per command workqueue won't buy us anything as the workqueue item would have to wait for the command abort to complete, which again is quite a waste. And concurrency would be hell; you'd have to flush the workqueue items for all outstanding if a device reset should attempted. And hope that no completion arrives at the time you're attempting to flush them. etc. I've been planning for asynchronous command aborts eventually, where using a per-command workqueue item comes in useful. Gut for now using existing callbacks makes life so much easier. And per-command workqueues will just complicate matters. Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@xxxxxxx +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg) -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
