On 7/13/18 2:05 AM, Ming Lei wrote: > Hi Guys, > > Runtime PM is usually enabled for SCSI devices, and we are switching to > SCSI_MQ recently, but runtime PM isn't supported yet by blk-mq, and > people may complain that. > > This patch tries to support runtime PM for blk-mq. And one chanllenge is > that it can be quite expensive to account the active in-flight IOs for > figuring out when to mark the last busy. This patch simply marks busy > after each non-PM IO is done, and this way is workable because: > > 1) pm_runtime_mark_last_busy() is very cheap > > 2) in-flight non-PM IO is checked in blk_pre_runtime_suspend(), so > if there is any IO queued, the device will be prevented from being > suspened. > > 3) Generally speaking, autosuspend_delay_ms is often big, and should > be in unit of second, so it shouldn't be a big deal to check if queue > is idle in blk_pre_runtime_suspend(). > > > V2: > - re-organize code as suggested by Christoph > - use seqlock to sync runtime PM and IO path See other mail on why this is not going to be acceptable. -- Jens Axboe
