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diff --git a/Documentation/block/queue-sysfs.rst b/Documentation/block/queue-sysfs.rst deleted file mode 100644 index 3f569d532485..000000000000 --- a/Documentation/block/queue-sysfs.rst +++ /dev/null @@ -1,321 +0,0 @@ -================= -Queue sysfs files -================= - -This text file will detail the queue files that are located in the sysfs tree -for each block device. Note that stacked devices typically do not export -any settings, since their queue merely functions as a remapping target. -These files are the ones found in the /sys/block/xxx/queue/ directory. - -Files denoted with a RO postfix are readonly and the RW postfix means -read-write. - -add_random (RW) ---------------- -This file allows to turn off the disk entropy contribution. Default -value of this file is '1'(on). - -chunk_sectors (RO) ------------------- -This has different meaning depending on the type of the block device. -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. - -dax (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. - -discard_granularity (RO) ------------------------- -This shows the size of internal allocation of the device in bytes, if -reported by the device. A value of '0' means device does not support -the discard functionality. - -discard_max_hw_bytes (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. - -discard_max_bytes (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. - -discard_zeroes_data (RO) ------------------------- -Obsolete. Always zero. - -fua (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. - -hw_sector_size (RO) -------------------- -This is the hardware sector size of the device, in bytes. - -io_poll (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. - -io_poll_delay (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. - -io_timeout (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. - -iostats (RW) -------------- -This file is used to control (on/off) the iostats accounting of the -disk. - -logical_block_size (RO) ------------------------ -This is the logical block size of the device, in bytes. - -max_discard_segments (RO) -------------------------- -The maximum number of DMA scatter/gather entries in a discard request. - -max_hw_sectors_kb (RO) ----------------------- -This is the maximum number of kilobytes supported in a single data transfer. - -max_integrity_segments (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. - -max_active_zones (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. - -max_open_zones (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. - -If the host attempts to exceed this limit, the driver should report this error -with BLK_STS_ZONE_OPEN_RESOURCE, which user space may see as the ETOOMANYREFS -errno. - -max_sectors_kb (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. - -max_segments (RO) ------------------ -Maximum number of elements in a DMA scatter/gather list that is submitted -to the associated block driver. - -max_segment_size (RO) ---------------------- -Maximum size in bytes of a single element in a DMA scatter/gather list. - -minimum_io_size (RO) --------------------- -This is the smallest preferred IO size reported by the device. - -nomerges (RW) -------------- -This enables the user to disable the lookup logic involved with IO -merging requests in the block layer. By default (0) all merges are -enabled. When set to 1 only simple one-hit merges will be tried. When -set to 2 no merge algorithms will be tried (including one-hit or more -complex tree/hash lookups). - -nr_requests (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. - -nr_zones (RO) -------------- -For zoned block devices (zoned attribute indicating "host-managed" or -"host-aware"), this indicates the total number of zones of the device. -This is always 0 for regular block devices. - -optimal_io_size (RO) --------------------- -This is the optimal IO size reported by the device. - -physical_block_size (RO) ------------------------- -This is the physical block size of device, in bytes. - -read_ahead_kb (RW) ------------------- -Maximum number of kilobytes to read-ahead for filesystems on this block -device. - -rotational (RW) ---------------- -This file is used to stat if the device is of rotational type or -non-rotational type. - -rq_affinity (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). - -scheduler (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. - -write_cache (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. - -write_same_max_bytes (RO) -------------------------- -This is the number of bytes the device can write in a single write-same -command. A value of '0' means write-same is not supported by this -device. - -wbt_lat_usec (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. - -throttle_sample_time (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. - -write_zeroes_max_bytes (RO) ---------------------------- -For block drivers that support REQ_OP_WRITE_ZEROES, the maximum number of -bytes that can be zeroed at once. The value 0 means that REQ_OP_WRITE_ZEROES -is not supported. - -zone_append_max_bytes (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. - -zoned (RO) ----------- -This 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". - -zone_write_granularity (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. - -independent_access_ranges (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/<device>/queue/independent_access_ranges/ - /sys/block/<device>/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. - -Jens Axboe <jens.axboe@oracle.com>, February 2009 |