Re: [PATCH v10 0/8] blk-mq: Implement runtime power management

[Ming Lei <ming.lei@redhat.com>]

On Fri, Sep 21, 2018 at 01:31:14PM -0700, Bart Van Assche wrote:
> Hello Jens,
> 
> One of the pieces that is missing before blk-mq can be made the default is
> implementing runtime power management support for blk-mq.  This patch series
> not only implements runtime power management for blk-mq but also fixes a
> starvation issue in the power management code for the legacy block
> layer. Please consider this patch series for the upstream kernel.
> 
> Thanks,
> 
> Bart.
> 
> Changes compared to v9:
> - Left out the patches that document the functions that iterate over requests
>   and also the patch that introduces blk_mq_queue_rq_iter().
> - Simplified blk_pre_runtime_suspend(): left out the check whether no requests
>   are in progress.
> - Fixed the race between blk_queue_enter(), queue freezing and runtime power
>   management that Ming had identified.
> - Added a new patch that introduces percpu_ref_resurrect().
> 
> Changes compared to v8:
> - Fixed the race that was reported by Jianchao.
> - Fixed another spelling issue in a source code comment.
> 
> Changes compared to v7:
> - Addressed Jianchao's feedback about patch "Make blk_get_request() block for
>   non-PM requests while suspended".
> - Added two new patches - one that documents the functions that iterate over
>   requests and one that introduces a new function that iterates over all
>   requests associated with a queue.
> 
> Changes compared to v6:
> - Left out the patches that split RQF_PREEMPT in three flags.
> - Left out the patch that introduces the SCSI device state SDEV_SUSPENDED.
> - Left out the patch that introduces blk_pm_runtime_exit().
> - Restored the patch that changes the PREEMPT_ONLY flag into a counter.
> 
> Changes compared to v5:
> - Introduced a new flag RQF_DV that replaces RQF_PREEMPT for SCSI domain
>   validation.
> - Introduced a new request queue state QUEUE_FLAG_DV_ONLY for SCSI domain
>   validation.
> - Instead of using SDEV_QUIESCE for both runtime suspend and SCSI domain
>   validation, use that state for domain validation only and introduce a new
>   state for runtime suspend, namely SDEV_QUIESCE.
> - Reallow system suspend during SCSI domain validation.
> - Moved the runtime resume call from the request allocation code into
>   blk_queue_enter().
> - Instead of relying on q_usage_counter, iterate over the tag set to determine
>   whether or not any requests are in flight.
> 
> Changes compared to v4:
> - Dropped the patches "Give RQF_PREEMPT back its original meaning" and
>   "Serialize queue freezing and blk_pre_runtime_suspend()".
> - Replaced "percpu_ref_read()" with "percpu_is_in_use()".
> - Inserted pm_request_resume() calls in the block layer request allocation
>   code such that the context that submits a request no longer has to call
>   pm_runtime_get().
> 
> Changes compared to v3:
> - Avoid adverse interactions between system-wide suspend/resume and runtime
>   power management by changing the PREEMPT_ONLY flag into a counter.
> - Give RQF_PREEMPT back its original meaning, namely that it is only set for
>   ide_preempt requests.
> - Remove the flag BLK_MQ_REQ_PREEMPT.
> - Removed the pm_request_resume() call.
> 
> Changes compared to v2:
> - Fixed the build for CONFIG_BLOCK=n.
> - Added a patch that introduces percpu_ref_read() in the percpu-counter code.
> - Added a patch that makes it easier to detect missing pm_runtime_get*() calls.
> - Addressed Jianchao's feedback including the comment about runtime overhead
>   of switching a per-cpu counter to atomic mode.
> 
> Changes compared to v1:
> - Moved the runtime power management code into a separate file.
> - Addressed Ming's feedback.
> 
> Bart Van Assche (8):
>   block: Move power management code into a new source file
>   block, scsi: Change the preempt-only flag into a counter
>   block: Split blk_pm_add_request() and blk_pm_put_request()
>   block: Schedule runtime resume earlier
>   percpu-refcount: Introduce percpu_ref_resurrect()
>   block: Allow unfreezing of a queue while requests are in progress
>   block: Make blk_get_request() block for non-PM requests while
>     suspended
>   blk-mq: Enable support for runtime power management
> 
>  block/Kconfig                   |   3 +
>  block/Makefile                  |   1 +
>  block/blk-core.c                | 270 ++++----------------------------
>  block/blk-mq-debugfs.c          |  10 +-
>  block/blk-mq.c                  |   4 +-
>  block/blk-pm.c                  | 216 +++++++++++++++++++++++++
>  block/blk-pm.h                  |  69 ++++++++
>  block/elevator.c                |  22 +--
>  drivers/scsi/scsi_lib.c         |  11 +-
>  drivers/scsi/scsi_pm.c          |   1 +
>  drivers/scsi/sd.c               |   1 +
>  drivers/scsi/sr.c               |   1 +
>  include/linux/blk-pm.h          |  24 +++
>  include/linux/blkdev.h          |  37 ++---
>  include/linux/percpu-refcount.h |   1 +
>  lib/percpu-refcount.c           |  28 +++-
>  16 files changed, 401 insertions(+), 298 deletions(-)
>  create mode 100644 block/blk-pm.c
>  create mode 100644 block/blk-pm.h
>  create mode 100644 include/linux/blk-pm.h
> 
> -- 
> 2.19.0.444.g18242da7ef-goog
> 

Looks fine,

Reviewed-by: Ming Lei <ming.lei@redhat.com>

thanks,
Ming