[PATCH v2 4/4] md/raid10: optimize check_decay_read_errors()

[linan666@xxxxxxxxxxxxxxx]

From: Li Nan <linan122@xxxxxxxxxx>

check_decay_read_errors() is used to handle rdev->read_errors. But
read_errors is inc and read after check_decay_read_errors() is invoked
in fix_read_error().

Put all operations of read_errors into check_decay_read_errors() and
clean up unnecessary atomic_read of read_errors.

Suggested-by: Yu Kuai <yukuai3@xxxxxxxxxx>
Signed-off-by: Li Nan <linan122@xxxxxxxxxx>
---
 drivers/md/raid10.c | 66 ++++++++++++++++++++++++---------------------
 1 file changed, 35 insertions(+), 31 deletions(-)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 4d615fcc6a50..79f94882227d 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -2655,39 +2655,53 @@ static void recovery_request_write(struct mddev *mddev, struct r10bio *r10_bio)
 }
 
 /*
- * Used by fix_read_error() to decay the per rdev read_errors.
+ * Used by fix_read_error() to decay the per rdev read_errors and check if
+ * read_error > max_read_errors.
  * We halve the read error count for every hour that has elapsed
  * since the last recorded read error.
  *
  */
-static void check_decay_read_errors(struct mddev *mddev, struct md_rdev *rdev)
+static bool check_decay_read_errors(struct mddev *mddev, struct md_rdev *rdev)
 {
-	long cur_time_mon;
+	time64_t cur_time_mon = ktime_get_seconds();
 	unsigned long hours_since_last;
-	unsigned int read_errors = atomic_read(&rdev->read_errors);
-
-	cur_time_mon = ktime_get_seconds();
+	unsigned int read_errors;
+	unsigned int max_read_errors =
+			atomic_read(&mddev->max_corr_read_errors);
 
 	if (rdev->last_read_error == 0) {
 		/* first time we've seen a read error */
 		rdev->last_read_error = cur_time_mon;
-		return;
-	}
+	} else {
+		hours_since_last = (long)(cur_time_mon -
+				    rdev->last_read_error) / 3600;
 
-	hours_since_last = (long)(cur_time_mon -
-			    rdev->last_read_error) / 3600;
+		rdev->last_read_error = cur_time_mon;
 
-	rdev->last_read_error = cur_time_mon;
+		/*
+		 * if hours_since_last is > the number of bits in read_errors
+		 * just set read errors to 0. We do this to avoid
+		 * overflowing the shift of read_errors by hours_since_last.
+		 */
+		read_errors = atomic_read(&rdev->read_errors);
+		if (hours_since_last >= 8 * sizeof(read_errors))
+			atomic_set(&rdev->read_errors, 0);
+		else
+			atomic_set(&rdev->read_errors,
+				   read_errors >> hours_since_last);
+	}
 
-	/*
-	 * if hours_since_last is > the number of bits in read_errors
-	 * just set read errors to 0. We do this to avoid
-	 * overflowing the shift of read_errors by hours_since_last.
-	 */
-	if (hours_since_last >= 8 * sizeof(read_errors))
-		atomic_set(&rdev->read_errors, 0);
-	else
-		atomic_set(&rdev->read_errors, read_errors >> hours_since_last);
+	read_errors = atomic_inc_return(&rdev->read_errors);
+	if (read_errors > max_read_errors) {
+		pr_notice("md/raid10:%s: %pg: Raid device exceeded read_error threshold [cur %u:max %u]\n",
+			  mdname(mddev), rdev->bdev, read_errors, max_read_errors);
+		pr_notice("md/raid10:%s: %pg: Failing raid device\n",
+			  mdname(mddev), rdev->bdev);
+		md_error(mddev, rdev);
+		return false;
+	}
+
+	return true;
 }
 
 static int r10_sync_page_io(struct md_rdev *rdev, sector_t sector,
@@ -2727,8 +2741,6 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
 	int sect = 0; /* Offset from r10_bio->sector */
 	int sectors = r10_bio->sectors;
 	struct md_rdev *rdev;
-	unsigned int max_read_errors =
-			atomic_read(&mddev->max_corr_read_errors);
 	int d = r10_bio->devs[r10_bio->read_slot].devnum;
 
 	/* still own a reference to this rdev, so it cannot
@@ -2741,15 +2753,7 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
 		   more fix_read_error() attempts */
 		return;
 
-	check_decay_read_errors(mddev, rdev);
-	atomic_inc(&rdev->read_errors);
-	if (atomic_read(&rdev->read_errors) > max_read_errors) {
-		pr_notice("md/raid10:%s: %pg: Raid device exceeded read_error threshold [cur %u:max %u]\n",
-			  mdname(mddev), rdev->bdev,
-			  atomic_read(&rdev->read_errors), max_read_errors);
-		pr_notice("md/raid10:%s: %pg: Failing raid device\n",
-			  mdname(mddev), rdev->bdev);
-		md_error(mddev, rdev);
+	if (check_decay_read_errors(mddev, rdev)) {
 		r10_bio->devs[r10_bio->read_slot].bio = IO_BLOCKED;
 		return;
 	}
-- 
2.31.1