[PATCH V2 01/13] block: estimate disk performance

[Shaohua Li]

weight based blk-throttling can use the estimated performance to
calculate cgroup bandwidth/IOPS. That said we never can't get accurate
disk performance in a complex workload, a roughly estimation is enough.

One issue is workload might not send enough IO to make disk 100% busy.
The calculation should compensate disk utilization. The calculation
equation is:
bps = (bytes * HZ / time) * (time / busy_time) = bytes * HZ / busy_time
iops = (ios * HZ / time) * (time / busy_time) = ios * HZ / busy_time

Signed-off-by: Shaohua Li <shli@xxxxxx>
---
 block/blk-core.c       | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++
 block/blk-sysfs.c      | 13 ++++++++++++
 include/linux/blkdev.h |  7 +++++++
 3 files changed, 76 insertions(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index ab51685..4244f28 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1919,6 +1919,59 @@ static inline int bio_check_eod(struct bio *bio, unsigned int nr_sectors)
 	return 0;
 }
 
+#define UPDATE_TIME (HZ / 2)
+static void blk_update_perf(struct request_queue *q,
+	struct hd_struct *p)
+{
+	unsigned long now = jiffies;
+	unsigned long last = q->bw_timestamp;
+	sector_t read_sect, write_sect, tmp_sect;
+	unsigned long read_ios, write_ios, tmp_ios;
+	unsigned long current_ticks;
+	unsigned int busy_ticks;
+
+	if (time_before(now, last + UPDATE_TIME))
+		return;
+
+	if (cmpxchg(&q->bw_timestamp, last, now) != last)
+		return;
+
+	tmp_sect = part_stat_read(p, sectors[READ]);
+	read_sect = tmp_sect - q->last_sects[READ];
+	q->last_sects[READ] = tmp_sect;
+	tmp_sect = part_stat_read(p, sectors[WRITE]);
+	write_sect = tmp_sect - q->last_sects[WRITE];
+	q->last_sects[WRITE] = tmp_sect;
+
+	tmp_ios = part_stat_read(p, ios[READ]);
+	read_ios = tmp_ios - q->last_ios[READ];
+	q->last_ios[READ] = tmp_ios;
+	tmp_ios = part_stat_read(p, ios[WRITE]);
+	write_ios = tmp_ios - q->last_ios[WRITE];
+	q->last_ios[WRITE] = tmp_ios;
+
+	current_ticks = part_stat_read(p, io_ticks);
+	busy_ticks = current_ticks - q->last_ticks;
+	q->last_ticks = current_ticks;
+
+	/* Don't account for long idle */
+	if (now - last > UPDATE_TIME * 2)
+		return;
+	/* Disk load is too low or driver doesn't account io_ticks */
+	if (busy_ticks == 0)
+		return;
+
+	if (busy_ticks > now - last)
+		busy_ticks = now - last;
+
+	tmp_sect = (read_sect + write_sect) * HZ;
+	sector_div(tmp_sect, busy_ticks);
+	q->disk_bw = tmp_sect;
+
+	tmp_ios = (read_ios + write_ios) * HZ / busy_ticks;
+	q->disk_iops = tmp_ios;
+}
+
 static noinline_for_stack bool
 generic_make_request_checks(struct bio *bio)
 {
@@ -1991,6 +2044,9 @@ generic_make_request_checks(struct bio *bio)
 	 */
 	create_io_context(GFP_ATOMIC, q->node);
 
+	blk_update_perf(q,
+		part->partno ? &part_to_disk(part)->part0 : part);
+
 	if (!blkcg_bio_issue_check(q, bio))
 		return false;
 
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index e140cc4..b59461c 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -348,6 +348,13 @@ static ssize_t queue_poll_store(struct request_queue *q, const char *page,
 	return ret;
 }
 
+static ssize_t queue_avg_perf_show(struct request_queue *q, char *page)
+{
+	return sprintf(page, "%llu %llu\n",
+		       (unsigned long long)q->disk_bw * 512,
+		       (unsigned long long)q->disk_iops);
+}
+
 static struct queue_sysfs_entry queue_requests_entry = {
 	.attr = {.name = "nr_requests", .mode = S_IRUGO | S_IWUSR },
 	.show = queue_requests_show,
@@ -479,6 +486,11 @@ static struct queue_sysfs_entry queue_poll_entry = {
 	.store = queue_poll_store,
 };
 
+static struct queue_sysfs_entry queue_avg_perf_entry = {
+	.attr = {.name = "average_perf", .mode = S_IRUGO },
+	.show = queue_avg_perf_show,
+};
+
 static struct attribute *default_attrs[] = {
 	&queue_requests_entry.attr,
 	&queue_ra_entry.attr,
@@ -504,6 +516,7 @@ static struct attribute *default_attrs[] = {
 	&queue_iostats_entry.attr,
 	&queue_random_entry.attr,
 	&queue_poll_entry.attr,
+	&queue_avg_perf_entry.attr,
 	NULL,
 };
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 29189ae..d2d6a7b 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -466,6 +466,13 @@ struct request_queue {
 	struct bio_set		*bio_split;
 
 	bool			mq_sysfs_init_done;
+
+	unsigned long bw_timestamp;
+	unsigned long last_ticks;
+	sector_t last_sects[2];
+	unsigned long last_ios[2];
+	sector_t disk_bw;
+	unsigned long disk_iops;
 };
 
 #define QUEUE_FLAG_QUEUED	1	/* uses generic tag queueing */
-- 
2.6.5