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| -rw-r--r-- | Documentation/ABI/stable/sysfs-block | 482 |
1 files changed, 381 insertions, 101 deletions
diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block index c70fce6b76c1..de3b86a3dfa5 100644 --- a/Documentation/ABI/stable/sysfs-block +++ b/Documentation/ABI/stable/sysfs-block @@ -46,7 +46,7 @@ Description: The value type is unsigned int. Cf. Documentation/block/stat.rst which contains a single value for requests in flight. - This is related to nr_requests in Documentation/block/queue-sysfs.rst + This is related to /sys/block/<disk>/queue/nr_requests and for SCSI device also its queue_depth. @@ -134,207 +134,487 @@ Description: same as the format of /sys/block/<disk>/stat. +What: /sys/block/<disk>/queue/add_random +Date: June 2010 +Contact: linux-block@vger.kernel.org +Description: + [RW] This file allows to turn off the disk entropy contribution. + Default value of this file is '1'(on). + + What: /sys/block/<disk>/queue/chunk_sectors Date: September 2016 Contact: Hannes Reinecke <hare@suse.com> Description: - chunk_sectors has different meaning depending on the type + [RO] chunk_sectors has different meaning depending on the type of the disk. For a RAID device (dm-raid), chunk_sectors - indicates the size in 512B sectors of the RAID volume - stripe segment. For a zoned block device, either - host-aware or host-managed, chunk_sectors indicates the - size in 512B sectors of the zones of the device, with - the eventual exception of the last zone of the device - which may be smaller. + indicates the size in 512B sectors of the RAID volume stripe + segment. For a zoned block device, either host-aware or + host-managed, chunk_sectors indicates the size in 512B sectors + of the zones of the device, with the eventual exception of the + last zone of the device which may be smaller. + + +What: /sys/block/<disk>/queue/dax +Date: June 2016 +Contact: linux-block@vger.kernel.org +Description: + [RO] This file indicates whether the device supports Direct + Access (DAX), used by CPU-addressable storage to bypass the + pagecache. It shows '1' if true, '0' if not. What: /sys/block/<disk>/queue/discard_granularity Date: May 2011 Contact: Martin K. Petersen <martin.petersen@oracle.com> Description: - Devices that support discard functionality may - internally allocate space using units that are bigger - than the logical block size. The discard_granularity - parameter indicates the size of the internal allocation - unit in bytes if reported by the device. Otherwise the - discard_granularity will be set to match the device's - physical block size. A discard_granularity of 0 means - that the device does not support discard functionality. + [RO] Devices that support discard functionality may internally + allocate space using units that are bigger than the logical + block size. The discard_granularity parameter indicates the size + of the internal allocation unit in bytes if reported by the + device. Otherwise the discard_granularity will be set to match + the device's physical block size. A discard_granularity of 0 + means that the device does not support discard functionality. What: /sys/block/<disk>/queue/discard_max_bytes Date: May 2011 Contact: Martin K. Petersen <martin.petersen@oracle.com> Description: - Devices that support discard functionality may have - internal limits on the number of bytes that can be - trimmed or unmapped in a single operation. Some storage - protocols also have inherent limits on the number of - blocks that can be described in a single command. The - discard_max_bytes parameter is set by the device driver - to the maximum number of bytes that can be discarded in - a single operation. Discard requests issued to the - device must not exceed this limit. A discard_max_bytes - value of 0 means that the device does not support - discard functionality. + [RW] While discard_max_hw_bytes is the hardware limit for the + device, this setting is the software limit. Some devices exhibit + large latencies when large discards are issued, setting this + value lower will make Linux issue smaller discards and + potentially help reduce latencies induced by large discard + operations. + + +What: /sys/block/<disk>/queue/discard_max_hw_bytes +Date: July 2015 +Contact: linux-block@vger.kernel.org +Description: + [RO] Devices that support discard functionality may have + internal limits on the number of bytes that can be trimmed or + unmapped in a single operation. The `discard_max_hw_bytes` + parameter is set by the device driver to the maximum number of + bytes that can be discarded in a single operation. Discard + requests issued to the device must not exceed this limit. A + `discard_max_hw_bytes` value of 0 means that the device does not + support discard functionality. What: /sys/block/<disk>/queue/discard_zeroes_data Date: May 2011 Contact: Martin K. Petersen <martin.petersen@oracle.com> Description: - Will always return 0. Don't rely on any specific behavior + [RO] Will always return 0. Don't rely on any specific behavior for discards, and don't read this file. +What: /sys/block/<disk>/queue/fua +Date: May 2018 +Contact: linux-block@vger.kernel.org +Description: + [RO] Whether or not the block driver supports the FUA flag for + write requests. FUA stands for Force Unit Access. If the FUA + flag is set that means that write requests must bypass the + volatile cache of the storage device. + + +What: /sys/block/<disk>/queue/hw_sector_size +Date: January 2008 +Contact: linux-block@vger.kernel.org +Description: + [RO] This is the hardware sector size of the device, in bytes. + + +What: /sys/block/<disk>/queue/independent_access_ranges/ +Date: October 2021 +Contact: linux-block@vger.kernel.org +Description: + [RO] The presence of this sub-directory of the + /sys/block/xxx/queue/ directory indicates that the device is + capable of executing requests targeting different sector ranges + in parallel. For instance, single LUN multi-actuator hard-disks + will have an independent_access_ranges directory if the device + correctly advertizes the sector ranges of its actuators. + + The independent_access_ranges directory contains one directory + per access range, with each range described using the sector + (RO) attribute file to indicate the first sector of the range + and the nr_sectors (RO) attribute file to indicate the total + number of sectors in the range starting from the first sector of + the range. For example, a dual-actuator hard-disk will have the + following independent_access_ranges entries.:: + + $ tree /sys/block/<disk>/queue/independent_access_ranges/ + /sys/block/<disk>/queue/independent_access_ranges/ + |-- 0 + | |-- nr_sectors + | `-- sector + `-- 1 + |-- nr_sectors + `-- sector + + The sector and nr_sectors attributes use 512B sector unit, + regardless of the actual block size of the device. Independent + access ranges do not overlap and include all sectors within the + device capacity. The access ranges are numbered in increasing + order of the range start sector, that is, the sector attribute + of range 0 always has the value 0. + + +What: /sys/block/<disk>/queue/io_poll +Date: November 2015 +Contact: linux-block@vger.kernel.org +Description: + [RW] When read, this file shows whether polling is enabled (1) + or disabled (0). Writing '0' to this file will disable polling + for this device. Writing any non-zero value will enable this + feature. + + +What: /sys/block/<disk>/queue/io_poll_delay +Date: November 2016 +Contact: linux-block@vger.kernel.org +Description: + [RW] If polling is enabled, this controls what kind of polling + will be performed. It defaults to -1, which is classic polling. + In this mode, the CPU will repeatedly ask for completions + without giving up any time. If set to 0, a hybrid polling mode + is used, where the kernel will attempt to make an educated guess + at when the IO will complete. Based on this guess, the kernel + will put the process issuing IO to sleep for an amount of time, + before entering a classic poll loop. This mode might be a little + slower than pure classic polling, but it will be more efficient. + If set to a value larger than 0, the kernel will put the process + issuing IO to sleep for this amount of microseconds before + entering classic polling. + + What: /sys/block/<disk>/queue/io_timeout Date: November 2018 Contact: Weiping Zhang <zhangweiping@didiglobal.com> Description: - io_timeout is the request timeout in milliseconds. If a request - does not complete in this time then the block driver timeout - handler is invoked. That timeout handler can decide to retry - the request, to fail it or to start a device recovery strategy. + [RW] io_timeout is the request timeout in milliseconds. If a + request does not complete in this time then the block driver + timeout handler is invoked. That timeout handler can decide to + retry the request, to fail it or to start a device recovery + strategy. + + +What: /sys/block/<disk>/queue/iostats +Date: January 2009 +Contact: linux-block@vger.kernel.org +Description: + [RW] This file is used to control (on/off) the iostats + accounting of the disk. What: /sys/block/<disk>/queue/logical_block_size Date: May 2009 Contact: Martin K. Petersen <martin.petersen@oracle.com> Description: - This is the smallest unit the storage device can - address. It is typically 512 bytes. + [RO] This is the smallest unit the storage device can address. + It is typically 512 bytes. What: /sys/block/<disk>/queue/max_active_zones Date: July 2020 Contact: Niklas Cassel <niklas.cassel@wdc.com> Description: - For zoned block devices (zoned attribute indicating + [RO] For zoned block devices (zoned attribute indicating "host-managed" or "host-aware"), the sum of zones belonging to any of the zone states: EXPLICIT OPEN, IMPLICIT OPEN or CLOSED, is limited by this value. If this value is 0, there is no limit. + If the host attempts to exceed this limit, the driver should + report this error with BLK_STS_ZONE_ACTIVE_RESOURCE, which user + space may see as the EOVERFLOW errno. + + +What: /sys/block/<disk>/queue/max_discard_segments +Date: February 2017 +Contact: linux-block@vger.kernel.org +Description: + [RO] The maximum number of DMA scatter/gather entries in a + discard request. + + +What: /sys/block/<disk>/queue/max_hw_sectors_kb +Date: September 2004 +Contact: linux-block@vger.kernel.org +Description: + [RO] This is the maximum number of kilobytes supported in a + single data transfer. + + +What: /sys/block/<disk>/queue/max_integrity_segments +Date: September 2010 +Contact: linux-block@vger.kernel.org +Description: + [RO] Maximum number of elements in a DMA scatter/gather list + with integrity data that will be submitted by the block layer + core to the associated block driver. + What: /sys/block/<disk>/queue/max_open_zones Date: July 2020 Contact: Niklas Cassel <niklas.cassel@wdc.com> Description: - For zoned block devices (zoned attribute indicating + [RO] For zoned block devices (zoned attribute indicating "host-managed" or "host-aware"), the sum of zones belonging to - any of the zone states: EXPLICIT OPEN or IMPLICIT OPEN, - is limited by this value. If this value is 0, there is no limit. + any of the zone states: EXPLICIT OPEN or IMPLICIT OPEN, is + limited by this value. If this value is 0, there is no limit. + + +What: /sys/block/<disk>/queue/max_sectors_kb +Date: September 2004 +Contact: linux-block@vger.kernel.org +Description: + [RW] This is the maximum number of kilobytes that the block + layer will allow for a filesystem request. Must be smaller than + or equal to the maximum size allowed by the hardware. + + +What: /sys/block/<disk>/queue/max_segment_size +Date: March 2010 +Contact: linux-block@vger.kernel.org +Description: + [RO] Maximum size in bytes of a single element in a DMA + scatter/gather list. + + +What: /sys/block/<disk>/queue/max_segments +Date: March 2010 +Contact: linux-block@vger.kernel.org +Description: + [RO] Maximum number of elements in a DMA scatter/gather list + that is submitted to the associated block driver. 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 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. + [RO] 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/nomerges Date: January 2010 Contact: linux-block@vger.kernel.org Description: - Standard I/O elevator operations include attempts to - merge contiguous I/Os. For known random I/O loads these - attempts will always fail and result in extra cycles - being spent in the kernel. This allows one to turn off - this behavior on one of two ways: When set to 1, complex - merge checks are disabled, but the simple one-shot merges - with the previous I/O request are enabled. When set to 2, - all merge tries are disabled. The default value is 0 - - which enables all types of merge tries. + [RW] Standard I/O elevator operations include attempts to merge + contiguous I/Os. For known random I/O loads these attempts will + always fail and result in extra cycles being spent in the + kernel. This allows one to turn off this behavior on one of two + ways: When set to 1, complex merge checks are disabled, but the + simple one-shot merges with the previous I/O request are + enabled. When set to 2, all merge tries are disabled. The + default value is 0 - which enables all types of merge tries. + + +What: /sys/block/<disk>/queue/nr_requests +Date: July 2003 +Contact: linux-block@vger.kernel.org +Description: + [RW] This controls how many requests may be allocated in the + block layer for read or write requests. Note that the total + allocated number may be twice this amount, since it applies only + to reads or writes (not the accumulated sum). + + To avoid priority inversion through request starvation, a + request queue maintains a separate request pool per each cgroup + when CONFIG_BLK_CGROUP is enabled, and this parameter applies to + each such per-block-cgroup request pool. IOW, if there are N + block cgroups, each request queue may have up to N request + pools, each independently regulated by nr_requests. What: /sys/block/<disk>/queue/nr_zones Date: November 2018 Contact: Damien Le Moal <damien.lemoal@wdc.com> Description: - nr_zones indicates the total number of zones of a zoned block - device ("host-aware" or "host-managed" zone model). For regular - block devices, the value is always 0. + [RO] nr_zones indicates the total number of zones of a zoned + block device ("host-aware" or "host-managed" zone model). For + regular block devices, the value is always 0. 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 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. + [RO] 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. If no optimal + I/O size is reported this file contains 0. 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 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. + [RO] 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/read_ahead_kb +Date: May 2004 +Contact: linux-block@vger.kernel.org +Description: + [RW] Maximum number of kilobytes to read-ahead for filesystems + on this block device. + + +What: /sys/block/<disk>/queue/rotational +Date: January 2009 +Contact: linux-block@vger.kernel.org +Description: + [RW] This file is used to stat if the device is of rotational + type or non-rotational type. + + +What: /sys/block/<disk>/queue/rq_affinity +Date: September 2008 +Contact: linux-block@vger.kernel.org +Description: + [RW] If this option is '1', the block layer will migrate request + completions to the cpu "group" that originally submitted the + request. For some workloads this provides a significant + reduction in CPU cycles due to caching effects. + + For storage configurations that need to maximize distribution of + completion processing setting this option to '2' forces the + completion to run on the requesting cpu (bypassing the "group" + aggregation logic). + + +What: /sys/block/<disk>/queue/scheduler +Date: October 2004 +Contact: linux-block@vger.kernel.org +Description: + [RW] When read, this file will display the current and available + IO schedulers for this block device. The currently active IO + scheduler will be enclosed in [] brackets. Writing an IO + scheduler name to this file will switch control of this block + device to that new IO scheduler. Note that writing an IO + scheduler name to this file will attempt to load that IO + scheduler module, if it isn't already present in the system. + + +What: /sys/block/<disk>/queue/throttle_sample_time +Date: March 2017 +Contact: linux-block@vger.kernel.org +Description: + [RW] This is the time window that blk-throttle samples data, in + millisecond. blk-throttle makes decision based on the + samplings. Lower time means cgroups have more smooth throughput, + but higher CPU overhead. This exists only when + CONFIG_BLK_DEV_THROTTLING_LOW is enabled. + + +What: /sys/block/<disk>/queue/wbt_lat_usec +Date: November 2016 +Contact: linux-block@vger.kernel.org +Description: + [RW] If the device is registered for writeback throttling, then + this file shows the target minimum read latency. If this latency + is exceeded in a given window of time (see wb_window_usec), then + the writeback throttling will start scaling back writes. Writing + a value of '0' to this file disables the feature. Writing a + value of '-1' to this file resets the value to the default + setting. + + +What: /sys/block/<disk>/queue/write_cache +Date: April 2016 +Contact: linux-block@vger.kernel.org +Description: + [RW] When read, this file will display whether the device has + write back caching enabled or not. It will return "write back" + for the former case, and "write through" for the latter. Writing + to this file can change the kernels view of the device, but it + doesn't alter the device state. This means that it might not be + safe to toggle the setting from "write back" to "write through", + since that will also eliminate cache flushes issued by the + kernel. What: /sys/block/<disk>/queue/write_same_max_bytes Date: January 2012 Contact: Martin K. Petersen <martin.petersen@oracle.com> Description: - Some devices support a write same operation in which a + [RO] Some devices support a write same operation in which a single data block can be written to a range of several - contiguous blocks on storage. This can be used to wipe - areas on disk or to initialize drives in a RAID - configuration. write_same_max_bytes indicates how many - bytes can be written in a single write same command. If - write_same_max_bytes is 0, write same is not supported - by the device. + contiguous blocks on storage. This can be used to wipe areas on + disk or to initialize drives in a RAID configuration. + write_same_max_bytes indicates how many bytes can be written in + a single write same command. If write_same_max_bytes is 0, write + same is not supported by the device. What: /sys/block/<disk>/queue/write_zeroes_max_bytes Date: November 2016 Contact: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com> Description: - Devices that support write zeroes operation in which a - single request can be issued to zero out the range of - contiguous blocks on storage without having any payload - in the request. This can be used to optimize writing zeroes - to the devices. write_zeroes_max_bytes indicates how many - bytes can be written in a single write zeroes command. If - write_zeroes_max_bytes is 0, write zeroes is not supported - by the device. + [RO] Devices that support write zeroes operation in which a + single request can be issued to zero out the range of contiguous + blocks on storage without having any payload in the request. + This can be used to optimize writing zeroes to the devices. + write_zeroes_max_bytes indicates how many bytes can be written + in a single write zeroes command. If write_zeroes_max_bytes is + 0, write zeroes is not supported by the device. + + +What: /sys/block/<disk>/queue/zone_append_max_bytes +Date: May 2020 +Contact: linux-block@vger.kernel.org +Description: + [RO] This is the maximum number of bytes that can be written to + a sequential zone of a zoned block device using a zone append + write operation (REQ_OP_ZONE_APPEND). This value is always 0 for + regular block devices. + + +What: /sys/block/<disk>/queue/zone_write_granularity +Date: January 2021 +Contact: linux-block@vger.kernel.org +Description: + [RO] This indicates the alignment constraint, in bytes, for + write operations in sequential zones of zoned block devices + (devices with a zoned attributed that reports "host-managed" or + "host-aware"). This value is always 0 for regular block devices. What: /sys/block/<disk>/queue/zoned Date: September 2016 Contact: Damien Le Moal <damien.lemoal@wdc.com> Description: - zoned indicates if the device is a zoned block device - and the zone model of the device if it is indeed zoned. - The possible values indicated by zoned are "none" for - regular block devices and "host-aware" or "host-managed" - for zoned block devices. The characteristics of - host-aware and host-managed zoned block devices are - described in the ZBC (Zoned Block Commands) and ZAC - (Zoned Device ATA Command Set) standards. These standards - also define the "drive-managed" zone model. However, - since drive-managed zoned block devices do not support - zone commands, they will be treated as regular block - devices and zoned will report "none". + [RO] zoned indicates if the device is a zoned block device and + the zone model of the device if it is indeed zoned. The + possible values indicated by zoned are "none" for regular block + devices and "host-aware" or "host-managed" for zoned block + devices. The characteristics of host-aware and host-managed + zoned block devices are described in the ZBC (Zoned Block + Commands) and ZAC (Zoned Device ATA Command Set) standards. + These standards also define the "drive-managed" zone model. + However, since drive-managed zoned block devices do not support + zone commands, they will be treated as regular block devices and + zoned will report "none". What: /sys/block/<disk>/stat |