On 02/07/2017 04:34 PM, Christoph Hellwig wrote: > On Tue, Feb 07, 2017 at 03:38:51PM +0100, Hannes Reinecke wrote: >> The SCSI passthrough commands pass in pre-formatted SGLs, so the driver >> just has to map them. >> If we were converting that we first have to re-format the >> (driver-specific) SGLs into linux sg lists, only to have them converted >> back into driver-specific ones once queuecommand is called. >> You sure it's worth the effort? >> >> The driver already reserves some tags for precisely this use-case, so it >> won't conflict with normal I/O operation. >> So where's the problem with that? > > If it was an entirely separate path that would be easy, but it's > not - see all the poking into the tag maps that your patch 8 > includes. If it was just a few tags on the side not interacting > with the scsi or blk-mq it wouldn't be such a problem. > But we do; we're getting the index/tag/smid from the high-priority list, which is separated from the normal SCSI I/O tag space. (which reminds me; there's another cleanup patch to be had in _ctl_do_mpt_command(), but that's beside the point). Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking 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)
