64 lines
2.3 KiB
Text
64 lines
2.3 KiB
Text
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Queue sysfs files
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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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Files denoted with a RO postfix are readonly and the RW postfix means
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read-write.
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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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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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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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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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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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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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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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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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Jens Axboe <jens.axboe@oracle.com>, February 2009
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