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| author | Leonid V. Fedorenchik <leonidsbox@gmail.com> | 2015-03-13 23:53:22 +0300 |
|---|---|---|
| committer | Jonathan Corbet <corbet@lwn.net> | 2015-03-20 07:41:56 -0600 |
| commit | 8962786ce3d91003bdd3f7c6bda2ee3641d66770 (patch) | |
| tree | 6f7f2753b75190324afbeab498d43a38c9442e6f /Documentation/block/biodoc.txt | |
| parent | d50ca07863eb42ab5acb11ae6b2241c3db875061 (diff) | |
Documentation: Remove mentioning of block barriers
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>
Diffstat (limited to 'Documentation/block/biodoc.txt')
| -rw-r--r-- | Documentation/block/biodoc.txt | 36 |
1 files changed, 9 insertions, 27 deletions
diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt index 5aabc08de811..fd12c0d835fd 100644 --- a/Documentation/block/biodoc.txt +++ b/Documentation/block/biodoc.txt @@ -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. - -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 +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 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 |