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Documentation: Remove mentioning of block barriers

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Remove mentioning of block barriers since they were removed.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Leonid V. Fedorenchik <leonidsbox@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Leonid V. Fedorenchik 2015-03-13 23:53:22 +03:00 committed by Jonathan Corbet
parent d50ca07863
commit 8962786ce3
1 changed files with 8 additions and 26 deletions
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34
Documentation/block/biodoc.txt
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@ -48,8 +48,7 @@ Description of Contents:
- Highmem I/O support
- I/O scheduler modularization
1.2 Tuning based on high level requirements/capabilities
1.2.1 I/O Barriers
1.2.2 Request Priority/Latency
1.2.1 Request Priority/Latency
1.3 Direct access/bypass to lower layers for diagnostics and special
device operations
1.3.1 Pre-built commands
@ -255,29 +254,12 @@ some control over i/o ordering.
What kind of support exists at the generic block layer for this ?
The flags and rw fields in the bio structure can be used for some tuning
from above e.g indicating that an i/o is just a readahead request, or for
marking barrier requests (discussed next), or priority settings (currently
unused). As far as user applications are concerned they would need an
additional mechanism either via open flags or ioctls, or some other upper
level mechanism to communicate such settings to block.
from above e.g indicating that an i/o is just a readahead request, or priority
settings (currently unused). As far as user applications are concerned they
would need an additional mechanism either via open flags or ioctls, or some
other upper level mechanism to communicate such settings to block.
1.2.1 I/O Barriers
There is a way to enforce strict ordering for i/os through barriers.
All requests before a barrier point must be serviced before the barrier
request and any other requests arriving after the barrier will not be
serviced until after the barrier has completed. This is useful for higher
level control on write ordering, e.g flushing a log of committed updates
to disk before the corresponding updates themselves.
A flag in the bio structure, BIO_BARRIER is used to identify a barrier i/o.
The generic i/o scheduler would make sure that it places the barrier request and
all other requests coming after it after all the previous requests in the
queue. Barriers may be implemented in different ways depending on the
driver. For more details regarding I/O barriers, please read barrier.txt
in this directory.
1.2.2 Request Priority/Latency
1.2.1 Request Priority/Latency
Todo/Under discussion:
Arjan's proposed request priority scheme allows higher levels some broad
@ -906,8 +888,8 @@ queue and specific I/O schedulers. Unless stated otherwise, elevator is used
to refer to both parts and I/O scheduler to specific I/O schedulers.
Block layer implements generic dispatch queue in block/*.c.
The generic dispatch queue is responsible for properly ordering barrier
requests, requeueing, handling non-fs requests and all other subtleties.
The generic dispatch queue is responsible for requeueing, handling non-fs
requests and all other subtleties.
Specific I/O schedulers are responsible for ordering normal filesystem
requests. They can also choose to delay certain requests to improve