Documentation / block / queue-sysfs.txt
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Based on kernel version 2.6.33. Page generated on 2010-02-24 15:35 EST.
1 Queue sysfs files 2 ================= 3 4 This text file will detail the queue files that are located in the sysfs tree 5 for each block device. Note that stacked devices typically do not export 6 any settings, since their queue merely functions are a remapping target. 7 These files are the ones found in the /sys/block/xxx/queue/ directory. 8 9 Files denoted with a RO postfix are readonly and the RW postfix means 10 read-write. 11 12 hw_sector_size (RO) 13 ------------------- 14 This is the hardware sector size of the device, in bytes. 15 16 max_hw_sectors_kb (RO) 17 ---------------------- 18 This is the maximum number of kilobytes supported in a single data transfer. 19 20 max_sectors_kb (RW) 21 ------------------- 22 This is the maximum number of kilobytes that the block layer will allow 23 for a filesystem request. Must be smaller than or equal to the maximum 24 size allowed by the hardware. 25 26 nomerges (RW) 27 ------------- 28 This enables the user to disable the lookup logic involved with IO merging 29 requests in the block layer. Merging may still occur through a direct 30 1-hit cache, since that comes for (almost) free. The IO scheduler will not 31 waste cycles doing tree/hash lookups for merges if nomerges is 1. Defaults 32 to 0, enabling all merges. 33 34 nr_requests (RW) 35 ---------------- 36 This controls how many requests may be allocated in the block layer for 37 read or write requests. Note that the total allocated number may be twice 38 this amount, since it applies only to reads or writes (not the accumulated 39 sum). 40 41 read_ahead_kb (RW) 42 ------------------ 43 Maximum number of kilobytes to read-ahead for filesystems on this block 44 device. 45 46 rq_affinity (RW) 47 ---------------- 48 If this option is enabled, the block layer will migrate request completions 49 to the CPU that originally submitted the request. For some workloads 50 this provides a significant reduction in CPU cycles due to caching effects. 51 52 scheduler (RW) 53 -------------- 54 When read, this file will display the current and available IO schedulers 55 for this block device. The currently active IO scheduler will be enclosed 56 in [] brackets. Writing an IO scheduler name to this file will switch 57 control of this block device to that new IO scheduler. Note that writing 58 an IO scheduler name to this file will attempt to load that IO scheduler 59 module, if it isn't already present in the system. 60 61 62 63 Jens Axboe <jens.axboe[AT]oracle[DOT]com>, February 2009
- [ block ]
- 00-INDEX
- barrier.txt
- biodoc.txt
- capability.txt
- data-integrity.txt
- deadline-iosched.txt
- ioprio.txt
- queue-sysfs.txt
- request.txt
- stat.txt
- switching-sched.txt
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