path: root/Documentation/block
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authorJens Axboe <jens.axboe@oracle.com>2009-02-02 13:02:31 +0100
committerJens Axboe <jens.axboe@oracle.com>2009-02-02 13:02:31 +0100
commitcbb5901b904e122139e97c6f4caed9b1f13c3455 (patch)
treeb8dc9f2f7108b54343d55169326f6d4eb333e498 /Documentation/block
parentc52440a69df22dca69794936a91e2fb529a707fb (diff)
block: add text file detailing queue/ sysfs files
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Diffstat (limited to 'Documentation/block')
1 files changed, 63 insertions, 0 deletions
diff --git a/Documentation/block/queue-sysfs.txt b/Documentation/block/queue-sysfs.txt
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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
+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. Merging may still occur through a direct
+1-hit cache, since that comes for (almost) free. The IO scheduler will not
+waste cycles doing tree/hash lookups for merges if nomerges is 1. Defaults
+to 0, enabling all merges.
+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
+read_ahead_kb (RW)
+Maximum number of kilobytes to read-ahead for filesystems on this block
+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