path: root/Documentation/block/queue-sysfs.txt
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authorAnton Arapov <>2012-04-16 10:05:28 +0200
committerAnton Arapov <>2012-04-16 10:05:28 +0200
commitb4b6116a13633898cf868f2f103c96a90c4c20f8 (patch)
tree93d1b7e2cfcdf473d8d4ff3ad141fa864f8491f6 /Documentation/block/queue-sysfs.txt
parentedd4be777c953e5faafc80d091d3084b4343f5d3 (diff)
fedora kernel: d9aad82f3319f3cfd1aebc01234254ef0c37ad84v3.3.2-1
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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. 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
+read_ahead_kb (RW)
+Maximum number of kilobytes to read-ahead for filesystems on this block
+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.
+Jens Axboe <>, February 2009