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+Queue sysfs files
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+=================
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+
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+This text file will detail the queue files that are located in the sysfs tree
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+for each block device. Note that stacked devices typically do not export
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+any settings, since their queue merely functions are a remapping target.
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+These files are the ones found in the /sys/block/xxx/queue/ directory.
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+
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+Files denoted with a RO postfix are readonly and the RW postfix means
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+read-write.
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+
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+hw_sector_size (RO)
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+-------------------
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+This is the hardware sector size of the device, in bytes.
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+
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+max_hw_sectors_kb (RO)
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+----------------------
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+This is the maximum number of kilobytes supported in a single data transfer.
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+
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+max_sectors_kb (RW)
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+-------------------
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+This is the maximum number of kilobytes that the block layer will allow
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+for a filesystem request. Must be smaller than or equal to the maximum
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+size allowed by the hardware.
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+
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+nomerges (RW)
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+-------------
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+This enables the user to disable the lookup logic involved with IO merging
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+requests in the block layer. Merging may still occur through a direct
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+1-hit cache, since that comes for (almost) free. The IO scheduler will not
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+waste cycles doing tree/hash lookups for merges if nomerges is 1. Defaults
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+to 0, enabling all merges.
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+
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+nr_requests (RW)
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+----------------
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+This controls how many requests may be allocated in the block layer for
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+read or write requests. Note that the total allocated number may be twice
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+this amount, since it applies only to reads or writes (not the accumulated
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+sum).
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+
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+read_ahead_kb (RW)
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+------------------
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+Maximum number of kilobytes to read-ahead for filesystems on this block
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+device.
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+
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+rq_affinity (RW)
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+----------------
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+If this option is enabled, the block layer will migrate request completions
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+to the CPU that originally submitted the request. For some workloads
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+this provides a significant reduction in CPU cycles due to caching effects.
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+
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+scheduler (RW)
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+--------------
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+When read, this file will display the current and available IO schedulers
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+for this block device. The currently active IO scheduler will be enclosed
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+in [] brackets. Writing an IO scheduler name to this file will switch
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+control of this block device to that new IO scheduler. Note that writing
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+an IO scheduler name to this file will attempt to load that IO scheduler
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+module, if it isn't already present in the system.
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+
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+
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+
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+Jens Axboe <jens.axboe@oracle.com>, February 2009
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Jens Axboe