Commit 7e5f5fb0 authored by Martin K. Petersen's avatar Martin K. Petersen Committed by Jens Axboe
Browse files

block: Update topology documentation 



Update topology comments and sysfs documentation based upon discussions
with Neil Brown.

Signed-off-by: default avatarMartin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent 70dd5bf3

Documentation/ABI/testing/sysfs-block

+23 −14
Original line number Diff line number Diff line
@@ -94,28 +94,37 @@ What: /sys/block/<disk>/queue/physical_block_size 
Date:		May 2009

Contact:	Martin K. Petersen <martin.petersen@oracle.com>

Description:

		This is the smallest unit the storage device can write

		without resorting to read-modify-write operation.  It is

		usually the same as the logical block size but may be

		bigger.  One example is SATA drives with 4KB sectors

		that expose a 512-byte logical block size to the

		operating system.

		This is the smallest unit a physical storage device can

		write atomically.  It is usually the same as the logical

		block size but may be bigger.  One example is SATA

		drives with 4KB sectors that expose a 512-byte logical

		block size to the operating system.  For stacked block

		devices the physical_block_size variable contains the

		maximum physical_block_size of the component devices.



What:		/sys/block/<disk>/queue/minimum_io_size

Date:		April 2009

Contact:	Martin K. Petersen <martin.petersen@oracle.com>

Description:

		Storage devices may report a preferred minimum I/O size,

		which is the smallest request the device can perform

		without incurring a read-modify-write penalty.  For disk

		drives this is often the physical block size.  For RAID

		arrays it is often the stripe chunk size.

		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.



What:		/sys/block/<disk>/queue/optimal_io_size

Date:		April 2009

Contact:	Martin K. Petersen <martin.petersen@oracle.com>

Description:

		Storage devices may report an optimal I/O size, which is

		the device's preferred unit of receiving I/O.  This is

		rarely reported for disk drives.  For RAID devices it is

		usually the stripe width or the internal block size.
 
		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.  If no optimal I/O size is

		reported this file contains 0.

block/blk-settings.c

+13 −6
Original line number Diff line number Diff line
@@ -413,10 +413,13 @@ EXPORT_SYMBOL(blk_limits_io_min); 
 * @min:  smallest I/O size in bytes

 *

 * Description:

 *   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

 *

 * Description:

 *   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)

{