Revert "block: remove artifical max_hw_sectors cap"

JeffMoyer · axboe · commit 30e2bc08b2bb · 2015-08-18T13:21:13.000-07:00
This reverts commit 34b48db. That commit caused performance regressions for streaming I/O workloads on a number of different storage devices, from SATA disks to external RAID arrays. It also managed to trip up some buggy firmware in at least one drive, causing data corruption. The next patch will bump the default max_sectors_kb value to 1280, which will accommodate a 10-data-disk stripe write with chunk size 128k. In the testing I've done using iozone, fio, and aio-stress, a value of 1280 does not show a big performance difference from 512. This will hopefully still help the software RAID setup that Christoph saw the original performance gains with while still not regressing other storage configurations. Signed-off-by: Jeff Moyer <jmoyer@redhat.com> Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/block/blk-settings.c b/block/blk-settings.c
@@ -236,7 +236,9 @@ void blk_limits_max_hw_sectors(struct queue_limits *limits, unsigned int max_hw_
 		       __func__, max_hw_sectors);
 	}
 
-	limits->max_sectors = limits->max_hw_sectors = max_hw_sectors;
+	limits->max_hw_sectors = max_hw_sectors;
+	limits->max_sectors = min_t(unsigned int, max_hw_sectors,
+				    BLK_DEF_MAX_SECTORS);
 }
 EXPORT_SYMBOL(blk_limits_max_hw_sectors);
 
diff --git a/drivers/block/aoe/aoeblk.c b/drivers/block/aoe/aoeblk.c
@@ -395,7 +395,7 @@ aoeblk_gdalloc(void *vp)
 	WARN_ON(d->flags & DEVFL_TKILL);
 	WARN_ON(d->gd);
 	WARN_ON(d->flags & DEVFL_UP);
-	blk_queue_max_hw_sectors(q, 1024);
+	blk_queue_max_hw_sectors(q, BLK_DEF_MAX_SECTORS);
 	q->backing_dev_info.name = "aoe";
 	q->backing_dev_info.ra_pages = READ_AHEAD / PAGE_CACHE_SIZE;
 	d->bufpool = mp;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
@@ -1132,6 +1132,7 @@ extern int blk_verify_command(unsigned char *cmd, fmode_t has_write_perm);
 enum blk_default_limits {
 	BLK_MAX_SEGMENTS	= 128,
 	BLK_SAFE_MAX_SECTORS	= 255,
+	BLK_DEF_MAX_SECTORS	= 1024,
 	BLK_MAX_SEGMENT_SIZE	= 65536,
 	BLK_SEG_BOUNDARY_MASK	= 0xFFFFFFFFUL,
 };

Original file line number	Diff line number	Diff line change
`@@ -236,7 +236,9 @@ void blk_limits_max_hw_sectors(struct queue_limits *limits, unsigned int max_hw_`
`236`	`236`	`__func__, max_hw_sectors);`
`237`	`237`	`}`
`238`	`238`
`239`		`- limits->max_sectors = limits->max_hw_sectors = max_hw_sectors;`
	`239`	`+ limits->max_hw_sectors = max_hw_sectors;`
	`240`	`+ limits->max_sectors = min_t(unsigned int, max_hw_sectors,`
	`241`	`+ BLK_DEF_MAX_SECTORS);`
`240`	`242`	`}`
`241`	`243`	`EXPORT_SYMBOL(blk_limits_max_hw_sectors);`
`242`	`244`