block: fix inaccurate io_ticks by set 'precise_iostat'

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5X6RT
CVE: NA

--------------------------------

After introducing commit 5b18b5a7 ("block: delete part_round_stats
and switch to less precise counting"), '%util' accounted by iostat
will be over reality data. In fact, the device is quite idle, but
iostat may show '%util' as a big number (e.g. 50%). It can produce by fio:

fio --name=1 --direct=1 --bs=4k --rw=read --filename=/dev/sda \
	   --thinktime=4ms --runtime=180
We fix this by using a switch(precise_iostat=1) to control whether or not
acconut ioticks precisely.

fixes: 5b18b5a7 ("block: delete part_round_stats and switch to less precise counting")
Signed-off-by: NZhang Wensheng <zhangwensheng5@huawei.com>
Signed-off-by: NYu Kuai <yukuai3@huawei.com>
Reviewed-by: NJason Yan <yanaijie@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

block/blk-core.c

@@ -62,6 +62,21 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(block_unplug);
 
 DEFINE_IDA(blk_queue_ida);
 
+bool precise_iostat;
+
+static int __init precise_iostat_setup(char *str)
+{
+	bool precise;
+
+	if (!strtobool(str, &precise)) {
+		precise_iostat = precise;
+		pr_info("precise iostat %d\n", precise_iostat);
+	}
+
+	return 1;
+}
+__setup("precise_iostat=", precise_iostat_setup);
+
 /*
  * For queue allocation
  */
@@ -1258,9 +1273,14 @@ void update_io_ticks(struct hd_struct *part, unsigned long now, bool end)
 	unsigned long stamp;
 again:
 	stamp = READ_ONCE(part->stamp);
-	if (unlikely(time_after(now, stamp))) {
-		if (likely(cmpxchg(&part->stamp, stamp, now) == stamp))
+	if (unlikely(time_after(now, stamp)) &&
+		likely(cmpxchg(&part->stamp, stamp, now) == stamp)) {
+		if (precise_iostat) {
+			if (end || part_in_flight(part))
+				__part_stat_add(part, io_ticks, now - stamp);
+		} else {
 			__part_stat_add(part, io_ticks, end ? now - stamp : 1);
+		}
 	}
 	if (part->partno) {
 		part = &part_to_disk(part)->part0;
@@ -1318,6 +1338,8 @@ void blk_account_io_done(struct request *req, u64 now)
 #else
 		part_stat_add(part, nsecs[sgrp], now - req->start_time_ns);
 #endif
+		if (precise_iostat)
+			part_stat_local_dec(part, in_flight[rq_data_dir(req)]);
 		part_stat_unlock();
 
 		hd_struct_put(part);
@@ -1333,6 +1355,8 @@ void blk_account_io_start(struct request *rq)
 
 	part_stat_lock();
 	update_io_ticks(rq->part, jiffies, false);
+	if (precise_iostat)
+		part_stat_local_inc(rq->part, in_flight[rq_data_dir(rq)]);
 	part_stat_unlock();
 }
 

block/blk-merge.c

@@ -696,6 +696,8 @@ static void blk_account_io_merge_request(struct request *req)
 	if (blk_do_io_stat(req)) {
 		part_stat_lock();
 		part_stat_inc(req->part, merges[op_stat_group(req_op(req))]);
+		if (precise_iostat)
+			part_stat_local_dec(req->part, in_flight[rq_data_dir(req)]);
 		part_stat_unlock();
 
 		hd_struct_put(req->part);

block/genhd.c

@@ -112,7 +112,7 @@ static void part_stat_read_all(struct hd_struct *part, struct disk_stats *stat)
 	}
 }
 
-static unsigned int part_in_flight(struct hd_struct *part)
+unsigned int part_in_flight(struct hd_struct *part)
 {
 	unsigned int inflight = 0;
 	int cpu;

include/linux/blkdev.h

@@ -29,6 +29,7 @@
 #include <linux/pm.h>
 #include <linux/sbitmap.h>
 
+extern bool precise_iostat;
 struct module;
 struct scsi_ioctl_command;
 

include/linux/genhd.h

@@ -304,6 +304,7 @@ extern void disk_part_iter_exit(struct disk_part_iter *piter);
 extern bool disk_has_partitions(struct gendisk *disk);
 
 /* block/genhd.c */
+extern unsigned int part_in_flight(struct hd_struct *part);
 extern void device_add_disk(struct device *parent, struct gendisk *disk,
 			    const struct attribute_group **groups);
 static inline void add_disk(struct gendisk *disk)