[RFC PATCH 1/2] block: introduce helper function to calculate bps budgt

["zhaoyang.huang" <zhaoyang.huang@xxxxxxxxxx>]

From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>

The 'over-sized' bio under blk throttle control will be delayed to
launch which breaks original IO timing and have the immediate BW be
not within the bps limit. Introduce a helper function to calculate block
device's budgt which provide the allowed bytes for current bio.

Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
---
 block/blk-throttle.c       | 44 ++++++++++++++++++++++++++++++++++++++
 include/linux/blk-cgroup.h | 10 +++++++++
 2 files changed, 54 insertions(+)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index f4850a6f860b..41c75258183d 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -10,6 +10,7 @@
 #include <linux/blkdev.h>
 #include <linux/bio.h>
 #include <linux/blktrace_api.h>
+#include <linux/cgroup.h>
 #include "blk.h"
 #include "blk-cgroup-rwstat.h"
 #include "blk-stat.h"
@@ -2365,6 +2366,49 @@ void blk_throtl_bio_endio(struct bio *bio)
 }
 #endif
 
+unsigned long blk_throttle_budgt(struct block_device *bdev)
+{
+	struct request_queue *q = bdev_get_queue(bdev);
+	struct blkcg *blkcg;
+	struct blkcg_gq *blkg;
+	struct throtl_grp *tg;
+	long long bytes_allowed = 0;
+	unsigned long jiffy_elapsed, jiffy_elapsed_rnd;
+	u64 bps_limit;
+
+	if (!q)
+		return U64_MAX;
+
+	rcu_read_lock();
+	spin_lock_irq(&q->queue_lock);
+	blkcg =	css_to_blkcg(task_css(current, io_cgrp_id));
+	if (!blkcg)
+		goto out;
+
+	blkg = blkg_lookup(blkcg, q);
+	if (!blkg || !blkg_tryget(blkg))
+		goto out;
+
+	tg = blkg_to_tg(blkg);
+	bps_limit = tg_bps_limit(tg, READ);
+	if (bps_limit == U64_MAX)
+		goto out;
+
+	jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[READ];
+	if (!jiffy_elapsed)
+		jiffy_elapsed_rnd = tg->td->throtl_slice;
+
+	jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, tg->td->throtl_slice);
+	bytes_allowed = calculate_bytes_allowed(bps_limit, jiffy_elapsed_rnd) +
+			tg->carryover_bytes[READ];
+	blkg_put(blkg);
+out:
+	spin_unlock_irq(&q->queue_lock);
+	rcu_read_unlock();
+	return bytes_allowed;
+}
+
+
 int blk_throtl_init(struct gendisk *disk)
 {
 	struct request_queue *q = disk->queue;
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index dd5841a42c33..ba79fa464e0a 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -15,10 +15,12 @@
  */
 
 #include <linux/types.h>
+#include <linux/limits.h>
 
 struct bio;
 struct cgroup_subsys_state;
 struct gendisk;
+struct block_device;
 
 #define FC_APPID_LEN              129
 
@@ -45,6 +47,14 @@ static inline struct cgroup_subsys_state *bio_blkcg_css(struct bio *bio)
 }
 #endif	/* CONFIG_BLK_CGROUP */
 
+#ifdef CONFIG_BLK_DEV_THROTTLING
+unsigned long blk_throttle_budgt(struct block_device *bdev);
+#else
+static inline unsigned long blk_throttle_budgt(struct block_device *bdev)
+{
+	return U64_MAX;
+}
+#endif
 int blkcg_set_fc_appid(char *app_id, u64 cgrp_id, size_t app_id_len);
 char *blkcg_get_fc_appid(struct bio *bio);
 
-- 
2.25.1