diff options
Diffstat (limited to 'Documentation/block')
| -rw-r--r-- | Documentation/block/as-iosched.txt | 6 | ||||
| -rw-r--r-- | Documentation/block/biodoc.txt | 10 |
2 files changed, 9 insertions, 7 deletions
diff --git a/Documentation/block/as-iosched.txt b/Documentation/block/as-iosched.txt index e2a66f8143c5..a598fe10a297 100644 --- a/Documentation/block/as-iosched.txt +++ b/Documentation/block/as-iosched.txt @@ -24,8 +24,10 @@ very similar behavior to the deadline IO scheduler. Selecting IO schedulers ----------------------- To choose IO schedulers at boot time, use the argument 'elevator=deadline'. -'noop' and 'as' (the default) are also available. IO schedulers are assigned -globally at boot time only presently. +'noop', 'as' and 'cfq' (the default) are also available. IO schedulers are +assigned globally at boot time only presently. It's also possible to change +the IO scheduler for a determined device on the fly, as described in +Documentation/block/switching-sched.txt. Anticipatory IO scheduler Policies diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt index 34bf8f60d8f8..c6c9a9c10d7f 100644 --- a/Documentation/block/biodoc.txt +++ b/Documentation/block/biodoc.txt @@ -183,7 +183,7 @@ it, the pci dma mapping routines and associated data structures have now been modified to accomplish a direct page -> bus translation, without requiring a virtual address mapping (unlike the earlier scheme of virtual address -> bus translation). So this works uniformly for high-memory pages (which -do not have a correponding kernel virtual address space mapping) and +do not have a corresponding kernel virtual address space mapping) and low-memory pages. Note: Please refer to DMA-mapping.txt for a discussion on PCI high mem DMA @@ -391,7 +391,7 @@ forced such requests to be broken up into small chunks before being passed on to the generic block layer, only to be merged by the i/o scheduler when the underlying device was capable of handling the i/o in one shot. Also, using the buffer head as an i/o structure for i/os that didn't originate -from the buffer cache unecessarily added to the weight of the descriptors +from the buffer cache unnecessarily added to the weight of the descriptors which were generated for each such chunk. The following were some of the goals and expectations considered in the @@ -403,14 +403,14 @@ i. Should be appropriate as a descriptor for both raw and buffered i/o - for raw i/o. ii. Ability to represent high-memory buffers (which do not have a virtual address mapping in kernel address space). -iii.Ability to represent large i/os w/o unecessarily breaking them up (i.e +iii.Ability to represent large i/os w/o unnecessarily breaking them up (i.e greater than PAGE_SIZE chunks in one shot) iv. At the same time, ability to retain independent identity of i/os from different sources or i/o units requiring individual completion (e.g. for latency reasons) v. Ability to represent an i/o involving multiple physical memory segments (including non-page aligned page fragments, as specified via readv/writev) - without unecessarily breaking it up, if the underlying device is capable of + without unnecessarily breaking it up, if the underlying device is capable of handling it. vi. Preferably should be based on a memory descriptor structure that can be passed around different types of subsystems or layers, maybe even @@ -1013,7 +1013,7 @@ Characteristics: i. Binary tree AS and deadline i/o schedulers use red black binary trees for disk position sorting and searching, and a fifo linked list for time-based searching. This -gives good scalability and good availablility of information. Requests are +gives good scalability and good availability of information. Requests are almost always dispatched in disk sort order, so a cache is kept of the next request in sort order to prevent binary tree lookups. |