Queue sysfs files

Based on kernel version 2.6.34. Page generated on 2010-05-31 16:02 EST.

	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. 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
	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[AT]oracle[DOT]com>, February 2009