On Tue, Nov 15 2005, Jens Axboe wrote: > On Tue, Nov 15 2005, Mike Christie wrote: > > Jens Axboe wrote: > > >On Tue, Nov 15 2005, Jeff Garzik wrote: > > > > > >>>For departure of libata from SCSI, I was thinking more of another more > > >>>generic block device framework in which libata can live in. And I > > >>>thought that it was reasonable to assume that the framework would supply > > >>>a EH mechanism which supports queue stalling/draining and separate > > >>>thread. So, my EH patches tried to make the same environment for libata > > >> > > >>A big reason why libata uses the SCSI layer is infrastructure like this. > > >>It would certainly be nice to see timeouts and EH at the block layer. > > >>The block layer itself already supports queue stalling/draining. > > > > > > > > >I have a pretty simple plan for this: > > > > > >- Add a timer to struct request. It already has a timeout field for > > > SG_IO originated requests, we could easily utilize this in general. > > > I'm not sure how the querying of timeout would happen so far, it would > > > probably require a q->set_rq_timeout() hook to ask the low level > > > driver to set/return rq->timeout for a given request. > > > > > >- Add a timeout hook to struct request_queue that would get invoked from > > > the timeout handler. Something along the lines of: > > > > > > - Timeout on a request happens. Freeze the queue and use > > > kblockd to take the actual timeout into process context, where > > > we call the queue ->rq_timeout() hook. Unfreeze/reschedule > > > queue operations based on what the ->rq_timeout() hook tells > > > us. > > > > > >That is generic enough to be able to arm the timeout automatically from > > >->elevator_activate_req_fn() and dearm it when it completes or gets > > >deactivated. It should also be possible to implement the SCSI error > > >handling on top of that. > > > > > > > To disable the timeout would you then have scsi_done call a block layer > > function to disarm it then follow the current flow where or do you think > > it would be nice to move the scsi softirq code up to block layer. So > > scsi_done would call a block layer function that would disarm the timer, > > add the request to a block layer softirq list (a list like scsi-ml's > > scsi_done_q), and then in the block layer softirq function it could call > > a request_queue callout which for scsi-ml's device queue would call > > scsi_decide_disposition and return if it wanted the request requeued or > > how many sectors completed or to kick off the eh. I had stated on this > > for my block layer multipath driver, but can seperate the patches if > > this would be useful. > > Yeah, that was part of my plan as well. I did post such a patch a year > or so ago, in a thread about decreasing ide completion latencies. > > > Would ide benefit from running from a softirq and would it be able to > > use such a thing? > > It's generally useful as it allows lock free completion from the irq > path, so that's goodness. I updated that patch, and converted IDE and SCSI to use it. See the results here: http://brick.kernel.dk/git/?p=linux-2.6-block.git;a=shortlog;h=blk-softirq The main change from the version posted last october is killing the 'slightly' overdesigned completion queue hashing. -- Jens Axboe - : 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
