[patch] remove gendisk->stamp_idle field

struct gendisk has these two fields: stamp, stamp_idle.  Update to
stamp_idle is always in sync with stamp and they are always the same.
Therefore, it does not add any value in having two fields tracking
same timestamp.  Suggest to remove it.

Also, we should only update gendisk stats with non-zero value.
Advantage is that we don't have to needlessly calculate memory address,
and then add zero to the content.
Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>
Signed-off-by: Jens Axboe <axboe@suse.de>

drivers/block/ll_rw_blk.c

@@ -2433,13 +2433,12 @@ void disk_round_stats(struct gendisk *disk)
 {
 	unsigned long now = jiffies;
 
-	__disk_stat_add(disk, time_in_queue,
-			disk->in_flight * (now - disk->stamp));
+	if (disk->in_flight) {
+		__disk_stat_add(disk, time_in_queue,
+				disk->in_flight * (now - disk->stamp));
+		__disk_stat_add(disk, io_ticks, (now - disk->stamp));
+	}
 	disk->stamp = now;
-
-	if (disk->in_flight)
-		__disk_stat_add(disk, io_ticks, (now - disk->stamp_idle));
-	disk->stamp_idle = now;
 }
 
 /*

fs/partitions/check.c

@@ -430,7 +430,7 @@ void del_gendisk(struct gendisk *disk)
 	disk->flags &= ~GENHD_FL_UP;
 	unlink_gendisk(disk);
 	disk_stat_set_all(disk, 0);
-	disk->stamp = disk->stamp_idle = 0;
+	disk->stamp = 0;
 
 	devfs_remove_disk(disk);
 

include/linux/genhd.h

@@ -119,7 +119,7 @@ struct gendisk {
 	int policy;
 
 	atomic_t sync_io;		/* RAID */
-	unsigned long stamp, stamp_idle;
+	unsigned long stamp;
 	int in_flight;
 #ifdef	CONFIG_SMP
 	struct disk_stats *dkstats;