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- 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 are 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.
- hw_sector_size (RO)
- -------------------
- This is the hardware sector size of the device, in bytes.
- max_hw_sectors_kb (RO)
- ----------------------
- This is the maximum number of kilobytes supported in a single data transfer.
- 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.
- 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).
- read_ahead_kb (RW)
- ------------------
- Maximum number of kilobytes to read-ahead for filesystems on this block
- device.
- rq_affinity (RW)
- ----------------
- If this option is enabled, the block layer will migrate request completions
- to the CPU that originally submitted the request. For some workloads
- this provides a significant reduction in CPU cycles due to caching effects.
- 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.
- Jens Axboe <jens.axboe@oracle.com>, February 2009
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