Tag preemption is the default behaviour, specifically blk_mq_get_tag()
will try to get tag unconditionally, which means a new io can preempt tag
even if there are lots of ios that are waiting for tags.
This patch introduce a new flag, prepare to disable such behaviour, in
order to optimize io performance for large random io for HHD.
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
block/blk-mq-debugfs.c | 1 +
block/blk-mq.h | 5 +++++
include/linux/blk-mq.h | 7 ++++++-
3 files changed, 12 insertions(+), 1 deletion(-)
diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index aa0349e9f083..f4228532ee3d 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -226,6 +226,7 @@ static const char *const hctx_flag_name[] = {
HCTX_FLAG_NAME(NO_SCHED),
HCTX_FLAG_NAME(STACKING),
HCTX_FLAG_NAME(TAG_HCTX_SHARED),
+ HCTX_FLAG_NAME(NO_TAG_PREEMPTION),
};
#undef HCTX_FLAG_NAME
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 2615bd58bad3..1a084b3b6097 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -168,6 +168,11 @@ static inline bool blk_mq_is_shared_tags(unsigned int flags)
return flags & BLK_MQ_F_TAG_HCTX_SHARED;
}
+static inline bool blk_mq_is_tag_preemptive(unsigned int flags)
+{
+ return !(flags & BLK_MQ_F_NO_TAG_PREEMPTION);
+}
+
static inline struct blk_mq_tags *blk_mq_tags_from_data(struct blk_mq_alloc_data *data)
{
if (!(data->rq_flags & RQF_ELV))
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 7aa5c54901a9..c9434162acc5 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -656,7 +656,12 @@ enum {
* or shared hwqs instead of 'mq-deadline'.
*/
BLK_MQ_F_NO_SCHED_BY_DEFAULT = 1 << 7,
- BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,
+ /*
+ * If the disk is under high io pressure, new io will wait directly
+ * without trying to preempt tag.
+ */
+ BLK_MQ_F_NO_TAG_PREEMPTION = 1 << 8,
+ BLK_MQ_F_ALLOC_POLICY_START_BIT = 9,
BLK_MQ_F_ALLOC_POLICY_BITS = 1,
BLK_MQ_S_STOPPED = 0,
--
2.31.1
