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Date: Thu, 20 Sep 2018 18:18:23 +0800
From: Jianchao Wang <jianchao.w.wang@...cle.com>
To: axboe@...nel.dk, tj@...nel.org, kent.overstreet@...il.com,
ming.lei@...hat.com, bart.vanassche@....com
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] block, scsi: rework the preempt only mode
Migrate preempt-only mode from queue_flags to queue_gate. Because
the queue_gate checking and __percpu_ref_get_many are under the
same sched rcu critical section, we don't need extra synchronize_sched
after blk_mq_freeze_queue any more.
Signed-off-by: Jianchao Wang <jianchao.w.wang@...cle.com>
---
block/blk-core.c | 32 ++++++++++----------------------
block/blk-mq-debugfs.c | 1 -
block/blk.h | 1 +
drivers/scsi/scsi_lib.c | 12 ++++--------
include/linux/blkdev.h | 3 ---
5 files changed, 15 insertions(+), 34 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index f8b8fe2..c8d642a 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -429,13 +429,13 @@ EXPORT_SYMBOL(blk_sync_queue);
*/
int blk_set_preempt_only(struct request_queue *q)
{
- return blk_queue_flag_test_and_set(QUEUE_FLAG_PREEMPT_ONLY, q);
+ return test_and_set_bit(BLK_QUEUE_GATE_PREEMPT_ONLY, &q->queue_gate);
}
EXPORT_SYMBOL_GPL(blk_set_preempt_only);
void blk_clear_preempt_only(struct request_queue *q)
{
- blk_queue_flag_clear(QUEUE_FLAG_PREEMPT_ONLY, q);
+ clear_bit(BLK_QUEUE_GATE_PREEMPT_ONLY, &q->queue_gate);
wake_up_all(&q->mq_freeze_wq);
}
EXPORT_SYMBOL_GPL(blk_clear_preempt_only);
@@ -919,6 +919,10 @@ static inline bool blk_queue_gate_allow(struct request_queue *q,
if (test_bit(BLK_QUEUE_GATE_FROZEN, &q->queue_gate))
return false;
+ if (test_bit(BLK_QUEUE_GATE_PREEMPT_ONLY, &q->queue_gate) &&
+ !(flags & BLK_MQ_REQ_PREEMPT))
+ return false;
+
return true;
}
@@ -929,39 +933,23 @@ static inline bool blk_queue_gate_allow(struct request_queue *q,
*/
int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)
{
- const bool preempt = flags & BLK_MQ_REQ_PREEMPT;
-
while (true) {
- bool success = false;
-
rcu_read_lock_sched();
if (blk_queue_gate_allow(q, flags)) {
__percpu_ref_get_many(&q->q_usage_counter, 1);
- /*
- * The code that sets the PREEMPT_ONLY flag is
- * responsible for ensuring that that flag is globally
- * visible before the queue is unfrozen.
- */
- if (preempt || !blk_queue_preempt_only(q)) {
- success = true;
- } else {
- percpu_ref_put(&q->q_usage_counter);
- }
+ rcu_read_unlock_sched();
+ return 0;
}
rcu_read_unlock_sched();
- if (success)
- return 0;
-
if (flags & BLK_MQ_REQ_NOWAIT)
return -EBUSY;
smp_rmb();
wait_event(q->mq_freeze_wq,
- (blk_queue_gate_allow(q, flags) &&
- (preempt || !blk_queue_preempt_only(q))) ||
- blk_queue_dying(q));
+ blk_queue_gate_allow(q, flags) ||
+ blk_queue_dying(q));
if (blk_queue_dying(q))
return -ENODEV;
}
diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index cb1e6cf..4174951 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -132,7 +132,6 @@ static const char *const blk_queue_flag_name[] = {
QUEUE_FLAG_NAME(REGISTERED),
QUEUE_FLAG_NAME(SCSI_PASSTHROUGH),
QUEUE_FLAG_NAME(QUIESCED),
- QUEUE_FLAG_NAME(PREEMPT_ONLY),
};
#undef QUEUE_FLAG_NAME
diff --git a/block/blk.h b/block/blk.h
index 19d2c00..e38060b 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -21,6 +21,7 @@ extern struct dentry *blk_debugfs_root;
enum blk_queue_gate_flag_t {
BLK_QUEUE_GATE_FROZEN,
+ BLK_QUEUE_GATE_PREEMPT_ONLY,
};
struct blk_flush_queue {
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 1980648..3c9c33a 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -3058,17 +3058,13 @@ scsi_device_quiesce(struct scsi_device *sdev)
WARN_ON_ONCE(sdev->quiesced_by && sdev->quiesced_by != current);
blk_set_preempt_only(q);
-
blk_mq_freeze_queue(q);
+ blk_mq_unfreeze_queue(q);
/*
- * Ensure that the effect of blk_set_preempt_only() will be visible
- * for percpu_ref_tryget() callers that occur after the queue
- * unfreeze even if the queue was already frozen before this function
- * was called. See also https://lwn.net/Articles/573497/.
+ * When we reach here:
+ * - PREEMPT_ONLY gate flag is globally visible
+ * - no non-preempt request in queue
*/
- synchronize_sched();
- blk_mq_unfreeze_queue(q);
-
mutex_lock(&sdev->state_mutex);
err = scsi_device_set_state(sdev, SDEV_QUIESCE);
if (err == 0)
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 9f3f0d7..caa73b8 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -700,7 +700,6 @@ struct request_queue {
#define QUEUE_FLAG_REGISTERED 26 /* queue has been registered to a disk */
#define QUEUE_FLAG_SCSI_PASSTHROUGH 27 /* queue supports SCSI commands */
#define QUEUE_FLAG_QUIESCED 28 /* queue has been quiesced */
-#define QUEUE_FLAG_PREEMPT_ONLY 29 /* only process REQ_PREEMPT requests */
#define QUEUE_FLAG_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \
(1 << QUEUE_FLAG_SAME_COMP) | \
@@ -738,8 +737,6 @@ bool blk_queue_flag_test_and_clear(unsigned int flag, struct request_queue *q);
((rq)->cmd_flags & (REQ_FAILFAST_DEV|REQ_FAILFAST_TRANSPORT| \
REQ_FAILFAST_DRIVER))
#define blk_queue_quiesced(q) test_bit(QUEUE_FLAG_QUIESCED, &(q)->queue_flags)
-#define blk_queue_preempt_only(q) \
- test_bit(QUEUE_FLAG_PREEMPT_ONLY, &(q)->queue_flags)
#define blk_queue_fua(q) test_bit(QUEUE_FLAG_FUA, &(q)->queue_flags)
extern int blk_set_preempt_only(struct request_queue *q);
--
2.7.4
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