On 03/26/2015 02:38 PM, Kashyap Desai wrote: > Hi Hannes, > > I was going through one of the slide posted at below link. > > http://events.linuxfoundation.org/sites/events/files/slides/SCSI-EH.pdf > > Slide #59 has below data. I was trying to correlate with latest upstream > code, but do not understand few things. Does Linux handle blocking I/O to > the device and target before it actually start legacy EH recovery ? Yes. This is handled by 'scsi_eh_scmd_add()', which adds the command to the internal 'eh_entry' list and starts recovery once all remaining outstanding commands are completed. > Also, how does linux scsi stack achieve task set abort ? > Currently we don't :-) The presentation was a roadmap about future EH updates. > Proposed SCSI EH strategy > • Send command aborts after timeout > • EH Recovery starts: > ‒ Block I/O to the device > ‒ Issue 'Task Set Abort' > ‒ Block I/O to the target > ‒ Issue I_T Nexus Reset > ‒ Complete outstanding command on success > ‒ Engage current EH strategy > ‒ LUN Reset, Target Reset etc > The current plans for EH updates are: - Convert eh_host_reset_handler() to take Scsi_Host as argument - Convert EH host reset to do a host rescan after try_host_reset() succeeded - Terminate failed scmds prior to calling try_host_reset() => with that we should be able to instantiate a quick failover when running under multipathing, as then I/Os will be returned prior to the host reset (which is know to take quite a long time) - Convert the remaining eh_XXX_reset_handler() to take the appropriate structure as argument. This will require some work, as some EH handler implementation re-use the command tag (or even the actual command) for sending TMFs. - Implementing a 'transport reset' EH function; to be called after the current EH LUN Reset - Investigating the possibilty for an asynchronous 'task set abort', and make the 'transport reset' EH function asynchronous, too. I've got a patchset for the first step, but the others still require some work ... Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@xxxxxxx +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (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
