diff options
Diffstat (limited to 'Documentation/block/deadline-iosched.txt')
| -rw-r--r-- | Documentation/block/deadline-iosched.txt | 25 |
1 files changed, 8 insertions, 17 deletions
diff --git a/Documentation/block/deadline-iosched.txt b/Documentation/block/deadline-iosched.txt index be08ffd1e9b8..c23cab13c3d1 100644 --- a/Documentation/block/deadline-iosched.txt +++ b/Documentation/block/deadline-iosched.txt | |||
| @@ -5,16 +5,10 @@ This little file attempts to document how the deadline io scheduler works. | |||
| 5 | In particular, it will clarify the meaning of the exposed tunables that may be | 5 | In particular, it will clarify the meaning of the exposed tunables that may be |
| 6 | of interest to power users. | 6 | of interest to power users. |
| 7 | 7 | ||
| 8 | Each io queue has a set of io scheduler tunables associated with it. These | 8 | Selecting IO schedulers |
| 9 | tunables control how the io scheduler works. You can find these entries | 9 | ----------------------- |
| 10 | in: | 10 | Refer to Documentation/block/switching-sched.txt for information on |
| 11 | 11 | selecting an io scheduler on a per-device basis. | |
| 12 | /sys/block/<device>/queue/iosched | ||
| 13 | |||
| 14 | assuming that you have sysfs mounted on /sys. If you don't have sysfs mounted, | ||
| 15 | you can do so by typing: | ||
| 16 | |||
| 17 | # mount none /sys -t sysfs | ||
| 18 | 12 | ||
| 19 | 13 | ||
| 20 | ******************************************************************************** | 14 | ******************************************************************************** |
| @@ -41,14 +35,11 @@ fifo_batch | |||
| 41 | 35 | ||
| 42 | When a read request expires its deadline, we must move some requests from | 36 | When a read request expires its deadline, we must move some requests from |
| 43 | the sorted io scheduler list to the block device dispatch queue. fifo_batch | 37 | the sorted io scheduler list to the block device dispatch queue. fifo_batch |
| 44 | controls how many requests we move, based on the cost of each request. A | 38 | controls how many requests we move. |
| 45 | request is either qualified as a seek or a stream. The io scheduler knows | ||
| 46 | the last request that was serviced by the drive (or will be serviced right | ||
| 47 | before this one). See seek_cost and stream_unit. | ||
| 48 | 39 | ||
| 49 | 40 | ||
| 50 | write_starved (number of dispatches) | 41 | writes_starved (number of dispatches) |
| 51 | ------------- | 42 | -------------- |
| 52 | 43 | ||
| 53 | When we have to move requests from the io scheduler queue to the block | 44 | When we have to move requests from the io scheduler queue to the block |
| 54 | device dispatch queue, we always give a preference to reads. However, we | 45 | device dispatch queue, we always give a preference to reads. However, we |
| @@ -73,6 +64,6 @@ that comes at basically 0 cost we leave that on. We simply disable the | |||
| 73 | rbtree front sector lookup when the io scheduler merge function is called. | 64 | rbtree front sector lookup when the io scheduler merge function is called. |
| 74 | 65 | ||
| 75 | 66 | ||
| 76 | Nov 11 2002, Jens Axboe <axboe@suse.de> | 67 | Nov 11 2002, Jens Axboe <jens.axboe@oracle.com> |
| 77 | 68 | ||
| 78 | 69 | ||