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Message-Id: <20230629121302.1124851-3-chengming.zhou@linux.dev>
Date: Thu, 29 Jun 2023 20:13:02 +0800
From: chengming.zhou@...ux.dev
To: axboe@...nel.dk, ming.lei@...hat.com, hch@....de, tj@...nel.org
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
Chengming Zhou <zhouchengming@...edance.com>
Subject: [PATCH v4 2/2] blk-mq: fix start_time_ns and alloc_time_ns for pre-allocated rq
From: Chengming Zhou <zhouchengming@...edance.com>
The iocost rely on rq start_time_ns and alloc_time_ns to tell saturation
state of the block device. Most of the time request is allocated after
rq_qos_throttle() and its alloc_time_ns or start_time_ns won't be affected.
But for plug batched allocation introduced by the commit 47c122e35d7e
("block: pre-allocate requests if plug is started and is a batch"), we can
rq_qos_throttle() after the allocation of the request. This is what the
blk_mq_get_cached_request() does.
In this case, the cached request alloc_time_ns or start_time_ns is much
ahead if blocked in any qos ->throttle().
This patch fix it by setting alloc_time_ns and start_time_ns to now
when the pre-allocated rq is actually used. And we skip setting the
alloc_time_ns and start_time_ns during pre-allocation, so just pass 0
in __blk_mq_alloc_requests_batch().
Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
---
block/blk-mq.c | 41 +++++++++++++++++++++++++++++++----------
block/blk-mq.h | 1 +
include/linux/blk-mq.h | 6 +++---
3 files changed, 35 insertions(+), 13 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index c50ef953759f..2849395ca4c6 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -337,6 +337,24 @@ void blk_rq_init(struct request_queue *q, struct request *rq)
}
EXPORT_SYMBOL(blk_rq_init);
+/* Set alloc and start time when pre-allocated rq is actually used */
+static inline void blk_mq_rq_time_init(struct request *rq)
+{
+ if (blk_mq_need_time_stamp(rq->rq_flags)) {
+ u64 now = ktime_get_ns();
+
+#ifdef CONFIG_BLK_RQ_ALLOC_TIME
+ /*
+ * The alloc time is only used by iocost for now,
+ * only possible when blk_mq_need_time_stamp().
+ */
+ if (blk_queue_rq_alloc_time(rq->q))
+ rq->alloc_time_ns = now;
+#endif
+ rq->start_time_ns = now;
+ }
+}
+
static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
struct blk_mq_tags *tags, unsigned int tag, u64 alloc_time_ns)
{
@@ -360,14 +378,11 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
}
rq->timeout = 0;
- if (blk_mq_need_time_stamp(rq))
- rq->start_time_ns = ktime_get_ns();
- else
- rq->start_time_ns = 0;
rq->part = NULL;
#ifdef CONFIG_BLK_RQ_ALLOC_TIME
rq->alloc_time_ns = alloc_time_ns;
#endif
+ rq->start_time_ns = data->start_time_ns;
rq->io_start_time_ns = 0;
rq->stats_sectors = 0;
rq->nr_phys_segments = 0;
@@ -397,8 +412,7 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
}
static inline struct request *
-__blk_mq_alloc_requests_batch(struct blk_mq_alloc_data *data,
- u64 alloc_time_ns)
+__blk_mq_alloc_requests_batch(struct blk_mq_alloc_data *data)
{
unsigned int tag, tag_offset;
struct blk_mq_tags *tags;
@@ -417,7 +431,7 @@ __blk_mq_alloc_requests_batch(struct blk_mq_alloc_data *data,
tag = tag_offset + i;
prefetch(tags->static_rqs[tag]);
tag_mask &= ~(1UL << i);
- rq = blk_mq_rq_ctx_init(data, tags, tag, alloc_time_ns);
+ rq = blk_mq_rq_ctx_init(data, tags, tag, 0);
rq_list_add(data->cached_rq, rq);
nr++;
}
@@ -488,9 +502,11 @@ static struct request *__blk_mq_alloc_requests(struct blk_mq_alloc_data *data)
* Try batched alloc if we want more than 1 tag.
*/
if (data->nr_tags > 1) {
- rq = __blk_mq_alloc_requests_batch(data, alloc_time_ns);
- if (rq)
+ rq = __blk_mq_alloc_requests_batch(data);
+ if (rq) {
+ blk_mq_rq_time_init(rq);
return rq;
+ }
data->nr_tags = 1;
}
@@ -514,6 +530,9 @@ static struct request *__blk_mq_alloc_requests(struct blk_mq_alloc_data *data)
goto retry;
}
+ if (blk_mq_need_time_stamp(data->rq_flags))
+ data->start_time_ns = ktime_get_ns();
+
return blk_mq_rq_ctx_init(data, blk_mq_tags_from_data(data), tag,
alloc_time_ns);
}
@@ -570,6 +589,7 @@ static struct request *blk_mq_alloc_cached_request(struct request_queue *q,
return NULL;
plug->cached_rq = rq_list_next(rq);
+ blk_mq_rq_time_init(rq);
}
rq->cmd_flags = opf;
@@ -1004,7 +1024,7 @@ static inline void __blk_mq_end_request_acct(struct request *rq, u64 now)
inline void __blk_mq_end_request(struct request *rq, blk_status_t error)
{
- if (blk_mq_need_time_stamp(rq))
+ if (blk_mq_need_time_stamp(rq->rq_flags))
__blk_mq_end_request_acct(rq, ktime_get_ns());
if (rq->end_io) {
@@ -2891,6 +2911,7 @@ static inline struct request *blk_mq_get_cached_request(struct request_queue *q,
plug->cached_rq = rq_list_next(rq);
rq_qos_throttle(q, *bio);
+ blk_mq_rq_time_init(rq);
rq->cmd_flags = (*bio)->bi_opf;
INIT_LIST_HEAD(&rq->queuelist);
return rq;
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 1743857e0b01..29ed4d05110e 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -150,6 +150,7 @@ struct blk_mq_alloc_data {
unsigned int shallow_depth;
blk_opf_t cmd_flags;
req_flags_t rq_flags;
+ u64 start_time_ns;
/* allocate multiple requests/tags in one go */
unsigned int nr_tags;
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index f401067ac03a..e8366e9c3388 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -834,9 +834,9 @@ void blk_mq_end_request_batch(struct io_comp_batch *ib);
* Only need start/end time stamping if we have iostat or
* blk stats enabled, or using an IO scheduler.
*/
-static inline bool blk_mq_need_time_stamp(struct request *rq)
+static inline bool blk_mq_need_time_stamp(req_flags_t rq_flags)
{
- return (rq->rq_flags & (RQF_IO_STAT | RQF_STATS | RQF_USE_SCHED));
+ return (rq_flags & (RQF_IO_STAT | RQF_STATS | RQF_USE_SCHED));
}
static inline bool blk_mq_is_reserved_rq(struct request *rq)
@@ -860,7 +860,7 @@ static inline bool blk_mq_add_to_batch(struct request *req,
iob->complete = complete;
else if (iob->complete != complete)
return false;
- iob->need_ts |= blk_mq_need_time_stamp(req);
+ iob->need_ts |= blk_mq_need_time_stamp(req->rq_flags);
rq_list_add(&iob->req_list, req);
return true;
}
--
2.39.2
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