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authorIngo Molnar <mingo@elte.hu>2009-01-31 17:32:31 +0100
committerIngo Molnar <mingo@elte.hu>2009-02-05 22:30:01 +0100
commit9d45cf9e36bf9bcf16df6e1cbf049807c8402823 (patch)
tree2118a16701418af10d215d2174df7ee0a5cbe6bd /Documentation/block/queue-sysfs.txt
parenta146649bc19d5eba4f5bfac6720c5f252d517a71 (diff)
parent0cd5c3c80a0ebd68c08312fa7d8c13149cc61c4c (diff)
downloadblackbird-op-linux-9d45cf9e36bf9bcf16df6e1cbf049807c8402823.tar.gz
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Merge branch 'x86/urgent' into x86/apic
Conflicts: arch/x86/mach-default/setup.c Semantic merge: arch/x86/kernel/irqinit_32.c Signed-off-by: Ingo Molnar <mingo@elte.hu>
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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. 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
+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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