[PATCH RFC 0/4] blk-mq: support runtime PM

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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().

Ming Lei (4):
  blk-mq: introduce blk_mq_support_runtime_pm()
  blk-mq: introduce blk_mq_pm_queue_idle()
  blk-mq: prepare for supporting runtime PM
  scsi_mq: enable runtime PM

 block/blk-core.c        | 14 +++++++++++---
 block/blk-mq.c          | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 block/blk-mq.h          |  3 +++
 drivers/scsi/scsi_lib.c |  3 ++-
 include/linux/blk-mq.h  | 10 ++++++++++
 5 files changed, 72 insertions(+), 4 deletions(-)

Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Cc: linux-pm@xxxxxxxxxxxxxxx
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Bart Van Assche <bart.vanassche@xxxxxxx>
Cc: "James E.J. Bottomley" <jejb@xxxxxxxxxxxxxxxxxx>
Cc: "Martin K. Petersen" <martin.petersen@xxxxxxxxxx>
Cc: linux-scsi@xxxxxxxxxxxxxxx


-- 
2.9.5




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