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Diffstat (limited to 'Documentation/block/queue-sysfs.txt')
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diff --git a/Documentation/block/queue-sysfs.txt b/Documentation/block/queue-sysfs.txt new file mode 100644 index 00000000000..e164403f60e --- /dev/null +++ b/Documentation/block/queue-sysfs.txt @@ -0,0 +1,63 @@ +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 |