On Fri, 2016-04-08 at 08:11 -0700, James Bottomley wrote: > On Fri, 2016-04-08 at 13:29 +0200, Hannes Reinecke wrote: > > Hi all, > > > > I'd like to propose a topic on block-mq issues with FC. > > During my performance testing using block/scsi-mq with FC I've hit > > several issues I'd like to discuss: > > > > - timeout handling: > > Out of necessity the status of any timed out command is undefined. > > So to be absolutely safe HBAs will be using extended timeouts here > > (eg 70secs for lpfc). During that time we _could_ signal I/O timeout > > to the upper layers, but then the tag will be reused, despite the > > HBA still having a reference to it. > > I'd like to discuss how this could be solved best with blk-mq. > > What's wrong with the obvious answer: the tag shouldn't be re-used > until after at least the TMF abort. If we need to escalate that then > it looks like the controller lost the tag and requires a bigger hammer. > > However, when I look at what we do, it seems the running abort handler > is triggered from the block timeout function, so where's the problem? > ... surely mq can't free the tag until that returns, because it might > extend the time. > > James There was some discussion a while back about whether we could decouple the SCSI EH's recovery of the device from using the failed scmds, so that once the disposition of the original I/O was determined (i.e. they had succeeded, failed or timed out & aborted), the scmds could be returned to a higher layer while the EH attempted to recover the device. That way, in a multipath environment, we could submit the I/O on working paths and avoid lengthy delays while we went through all the resets. We still need a successful abort after a timeout, but at least in the above scenario we shouldn't be reusing the tags until the device is recovered, as further I/O should be blocked while EH is running. -Ewan -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
