From: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
iocost rely on rq start_time_ns and alloc_time_ns to tell the saturation
state of the block device.
If any qos ->throttle() end up blocking, the cached rq start_time_ns and
alloc_time_ns will include its throtted time, which can confuse its user.
This patch add nr_flush counter in blk_plug, so we can tell if the task
has throttled in any qos ->throttle(), in which case we need to correct
the rq start_time_ns and alloc_time_ns.
Another solution may be make rq_qos_throttle() return bool to indicate
if it has throttled in any qos ->throttle(). But this need more changes.
Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
---
block/blk-core.c | 3 +++
block/blk-mq.c | 18 ++++++++++++++++++
include/linux/blkdev.h | 8 +++++---
3 files changed, 26 insertions(+), 3 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index 00c74330fa92..5109f7f5606c 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1053,6 +1053,7 @@ void blk_start_plug_nr_ios(struct blk_plug *plug, unsigned short nr_ios)
plug->cached_rq = NULL;
plug->nr_ios = min_t(unsigned short, nr_ios, BLK_MAX_REQUEST_COUNT);
plug->rq_count = 0;
+ plug->nr_flush = 0;
plug->multiple_queues = false;
plug->has_elevator = false;
plug->nowait = false;
@@ -1150,6 +1151,8 @@ void __blk_flush_plug(struct blk_plug *plug, bool from_schedule)
*/
if (unlikely(!rq_list_empty(plug->cached_rq)))
blk_mq_free_plug_rqs(plug);
+
+ plug->nr_flush++;
}
/**
diff --git a/block/blk-mq.c b/block/blk-mq.c
index f6dad0886a2f..8731f2815790 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2871,6 +2871,7 @@ static inline struct request *blk_mq_get_cached_request(struct request_queue *q,
{
struct request *rq;
enum hctx_type type, hctx_type;
+ unsigned short nr_flush;
if (!plug)
return NULL;
@@ -2897,8 +2898,25 @@ static inline struct request *blk_mq_get_cached_request(struct request_queue *q,
* before we throttle.
*/
plug->cached_rq = rq_list_next(rq);
+ nr_flush = plug->nr_flush;
rq_qos_throttle(q, *bio);
+ /*
+ * If any qos ->throttle() end up blocking, we will have flushed the
+ * plug and we need to correct the rq start_time_ns and alloc_time_ns.
+ */
+ if (nr_flush != plug->nr_flush) {
+ if (blk_mq_need_time_stamp(rq)) {
+ u64 now = ktime_get_ns();
+
+#ifdef CONFIG_BLK_RQ_ALLOC_TIME
+ if (rq->alloc_time_ns)
+ rq->alloc_time_ns += now - rq->start_time_ns;
+#endif
+ rq->start_time_ns = now;
+ }
+ }
+
rq->cmd_flags = (*bio)->bi_opf;
INIT_LIST_HEAD(&rq->queuelist);
return rq;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index e3242e67a8e3..cf66871a1844 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -978,9 +978,11 @@ struct blk_plug {
unsigned short rq_count;
- bool multiple_queues;
- bool has_elevator;
- bool nowait;
+ unsigned short nr_flush;
+
+ bool multiple_queues:1;
+ bool has_elevator:1;
+ bool nowait:1;
struct list_head cb_list; /* md requires an unplug callback */
};
--
2.39.2
