On 07/18/2018 02:06 PM, Ming Lei wrote: > On Wed, Jul 18, 2018 at 5:49 AM, Jens Axboe <axboe@xxxxxxxxx> wrote: >> On 7/17/18 9:38 AM, Ming Lei wrote: >>> On Tue, Jul 17, 2018 at 03:34:35PM +0000, Bart Van Assche wrote: >>>> On Tue, 2018-07-17 at 23:30 +0800, Ming Lei wrote: >>>>> On Tue, Jul 17, 2018 at 03:24:11PM +0200, Christoph Hellwig wrote: >>>>>> On Fri, Jul 13, 2018 at 04:06:02PM +0800, Ming Lei wrote: >>>>>>> Usually SCSI supports runtime PM, so pass BLK_MQ_F_SUPPORT_RPM to blk-mq >>>>>>> core for enabling block runtime PM. >>>>>> >>>>>> I still think enabling this unconditionally for any SCSI device was >>>>>> a mistake, and it is even more so for blk-mq. >>>>>> >>>>>> Please only opt in for ufs, ATA first, adding others if wanted by >>>>>> maintainers. >>>>> >>>>> No, this way will cause regression because runtime PM works for >>>>> all sd/sr device actually, and it isn't related with scsi host. >>>> >>>> For which SCSI devices other than ufs and ATA do we need PM support? >>> >>> As I said, it is any sd/sr device, which can be put down by runtime PM >>> via START_STOP command if it isn't used for a while. >> >> Christoph is basically echoing my concerns. Why don't we just enable >> it on slower devices, similarly to what we do for adding >> randomness? Nobody wants to pay this overhead for faster devices, >> since most people won't care. > > IMO the problem isn't related with slow or quick device, it is related with > the system, especially when it cares about power consumption, such as > mobile phone, or laptop or servers with lots of disks attached. And we know > it is often to see some fast disks shipped in laptop, such as NVMe, or other > SSD. > But those typically have dedicated (transport/driver) mechanism to put the device to sleep, _and_ START STOP UNIT will be emulated for those devices anyway. I'd rather advocate to move runtime PM into the individual subsystems/drivers, and _not_ abuse START STOP UNIT here. 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)
