Hi all
The current queue freeze depending on percpu_ref_kil/reinit has a limit that
we have drain the requests before unfreeze the queue.
Let's rework the queue freeze feature as following:
1. introduce __percpu_ref_get_many.
It is same with original percpu_ref_get_many, but just need callers to provide
sched rcu critical section. We will put the __percpu_ref_get_many and our own
condition checking under rcu_read_lock_sched. With this new helper interface,
we could save an extra rcu_read_lock_sched.
2. rework the blk_queue_enter as:
rcu_read_lock_sched()
if condition check true
__percpu_ref_get_many(&q->q_usage_counter, 1)
else
goto wait
rcu_read_unlock_sched()
3. use percpu_ref_switch_to_atomic/percpu to switch mode directly.
Then we could unfreeze the queue w/o draining requests.
In addition, preempt-only mode code could be simplified.
Jianchao Wang (3)
percpu_ref: add a new helper interface
blk-core: rework the queue freeze
block, scsi: rework the preempt only mode
d16c830226a0ac15cb5947479030b
block/blk-core.c | 58 ++++++++++++++++++++++++++--------------------------------
block/blk-mq-debugfs.c | 1 -
block/blk-mq.c | 8 ++++++--
block/blk.h | 5 +++++
drivers/scsi/scsi_lib.c | 12 ++++--------
include/linux/blkdev.h | 5 ++---
include/linux/percpu-refcount.h | 23 +++++++++++++++++------
7 files changed, 60 insertions(+), 52 deletions(-)
Thanks
Jianchao
