| 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 '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 <jens.axboe@oracle.com>, February 2009 |
