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authorMauro Carvalho Chehab <mchehab@osg.samsung.com>2015-04-21 11:33:03 +0200
committerMauro Carvalho Chehab <mchehab@osg.samsung.com>2015-04-21 14:44:55 +0200
commit64131a87f2aae2ed9e05d8227c5b009ca6c50d98 (patch)
treefdea23fd59216120bf54a48c60ca24489a733f14 /Documentation/block/biodoc.txt
parentMerge branch 'patchwork' into v4l_for_linus (diff)
parentMerge Linus master into drm-next (diff)
downloadlinux-64131a87f2aae2ed9e05d8227c5b009ca6c50d98.tar.xz
linux-64131a87f2aae2ed9e05d8227c5b009ca6c50d98.zip
Merge branch 'drm-next-merged' of git://people.freedesktop.org/~airlied/linux into v4l_for_linus
* 'drm-next-merged' of git://people.freedesktop.org/~airlied/linux: (9717 commits) media-bus: Fixup RGB444_1X12, RGB565_1X16, and YUV8_1X24 media bus format hexdump: avoid warning in test function fs: take i_mutex during prepare_binprm for set[ug]id executables smp: Fix error case handling in smp_call_function_*() iommu-common: Fix PARISC compile-time warnings sparc: Make LDC use common iommu poll management functions sparc: Make sparc64 use scalable lib/iommu-common.c functions Break up monolithic iommu table/lock into finer graularity pools and lock sparc: Revert generic IOMMU allocator. tools/power turbostat: correct dumped pkg-cstate-limit value tools/power turbostat: calculate TSC frequency from CPUID(0x15) on SKL tools/power turbostat: correct DRAM RAPL units on recent Xeon processors tools/power turbostat: Initial Skylake support tools/power turbostat: Use $(CURDIR) instead of $(PWD) and add support for O= option in Makefile tools/power turbostat: modprobe msr, if needed tools/power turbostat: dump MSR_TURBO_RATIO_LIMIT2 tools/power turbostat: use new MSR_TURBO_RATIO_LIMIT names Bluetooth: hidp: Fix regression with older userspace and flags validation config: Enable NEED_DMA_MAP_STATE by default when SWIOTLB is selected perf/x86/intel/pt: Fix and clean up error handling in pt_event_add() ... That solves several merge conflicts: Documentation/DocBook/media/v4l/subdev-formats.xml Documentation/devicetree/bindings/vendor-prefixes.txt drivers/staging/media/mn88473/mn88473.c include/linux/kconfig.h include/uapi/linux/media-bus-format.h The ones at subdev-formats.xml and media-bus-format.h are not trivial. That's why we opted to merge from DRM.
Diffstat (limited to 'Documentation/block/biodoc.txt')
-rw-r--r--Documentation/block/biodoc.txt36
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