|author||Martin K. Petersen <email@example.com>||2009-07-31 11:49:13 -0400|
|committer||Jens Axboe <firstname.lastname@example.org>||2009-08-01 10:24:35 +0200|
block: Update topology documentation
Update topology comments and sysfs documentation based upon discussions with Neil Brown. Signed-off-by: Martin K. Petersen <email@example.com> Signed-off-by: Jens Axboe <firstname.lastname@example.org>
Diffstat (limited to 'block/blk-settings.c')
1 files changed, 13 insertions, 6 deletions
diff --git a/block/blk-settings.c b/block/blk-settings.c
index e1327ddfc13..476d8706507 100644
@@ -413,10 +413,13 @@ EXPORT_SYMBOL(blk_limits_io_min);
* @min: smallest I/O size in bytes
- * Some devices have an internal block size bigger than the reported
- * hardware sector size. This function can be used to signal the
- * smallest I/O the device can perform without incurring a performance
- * penalty.
+ * Storage devices may report a granularity or preferred minimum I/O
+ * size which is the smallest request the device can perform without
+ * incurring a performance penalty. For disk drives this is often the
+ * physical block size. For RAID arrays it is often the stripe chunk
+ * size. A properly aligned multiple of minimum_io_size is the
+ * preferred request size for workloads where a high number of I/O
+ * operations is desired.
void blk_queue_io_min(struct request_queue *q, unsigned int min)
@@ -430,8 +433,12 @@ EXPORT_SYMBOL(blk_queue_io_min);
* @opt: optimal request size in bytes
- * Drivers can call this function to set the preferred I/O request
- * size for devices that report such a value.
+ * Storage devices may report an optimal I/O size, which is the
+ * device's preferred unit for sustained I/O. This is rarely reported
+ * for disk drives. For RAID arrays it is usually the stripe width or
+ * the internal track size. A properly aligned multiple of
+ * optimal_io_size is the preferred request size for workloads where
+ * sustained throughput is desired.
void blk_queue_io_opt(struct request_queue *q, unsigned int opt)