On Fri, 2017-04-21 at 22:31 +0000, Song Liu wrote: > On Apr 21, 2017, at 2:20 PM, Bart Van Assche <[email protected]> > wrote: > > On Fri, 2017-04-21 at 14:13 -0700, Song Liu wrote: > > > On the other hand, some devices do long latency IO during deletion, > > > for example, sd_shutdown() may do sync cache and/or start_stop. > > > It is not necessary for these commands to run in series. > > > > Have you noticed my patch series that makes sd_shutdown() submit the > > SYNCHRONIZE CACHE command asynchronously? Have you tried whether that > > patch series would be a good alternative? > > The asynchronous SYNCHRONIZE CACHE will not help our use case, where the > latency comes from sd_start_stop_device(). Seems it is not easy to make > the START STOP UNIT command async.
Hello Song, It should be possible to make the START STOP UNIT command asynchronous too by issuing it asynchronously from inside sd_sync_cache_done(). To avoid dereferencing a stale struct scsi_disk pointer you will either have to hold an additional reference as long as the SYNCHRONIZE CACHE command is in progress or copy the data needed from struct scsi_disk into the SCSI request. Bart.
