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| author | Changbin Du <changbin.du@gmail.com> | 2019-05-08 23:21:32 +0800 |
|---|---|---|
| committer | Jonathan Corbet <corbet@lwn.net> | 2019-05-08 14:34:11 -0600 |
| commit | 9d12f58fe91e5e72ef08afe9e3e66d1c755fc085 (patch) | |
| tree | b6a978c0c86478e81fe351a2bb5dd67c4452c502 /Documentation/x86 | |
| parent | 1cd7af509dc223905dce622c07ec62e26044e3c0 (diff) | |
| download | lwn-9d12f58fe91e5e72ef08afe9e3e66d1c755fc085.tar.gz lwn-9d12f58fe91e5e72ef08afe9e3e66d1c755fc085.zip | |
Documentation: x86: convert orc-unwinder.txt to reST
This converts the plain text documentation to reStructuredText format and
add it to Sphinx TOC tree. No essential content change.
Signed-off-by: Changbin Du <changbin.du@gmail.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/x86')
| -rw-r--r-- | Documentation/x86/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/x86/orc-unwinder.rst (renamed from Documentation/x86/orc-unwinder.txt) | 27 |
2 files changed, 16 insertions, 12 deletions
diff --git a/Documentation/x86/index.rst b/Documentation/x86/index.rst index 6e3c887a0c3b..453557097743 100644 --- a/Documentation/x86/index.rst +++ b/Documentation/x86/index.rst @@ -14,6 +14,7 @@ x86-specific Documentation kernel-stacks entry_64 earlyprintk + orc-unwinder zero-page tlb mtrr diff --git a/Documentation/x86/orc-unwinder.txt b/Documentation/x86/orc-unwinder.rst index cd4b29be29af..d811576c1f3e 100644 --- a/Documentation/x86/orc-unwinder.txt +++ b/Documentation/x86/orc-unwinder.rst @@ -1,8 +1,11 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============ ORC unwinder ============ Overview --------- +======== The kernel CONFIG_UNWINDER_ORC option enables the ORC unwinder, which is similar in concept to a DWARF unwinder. The difference is that the @@ -23,12 +26,12 @@ correlate instruction addresses with their stack states at run time. ORC vs frame pointers ---------------------- +===================== With frame pointers enabled, GCC adds instrumentation code to every function in the kernel. The kernel's .text size increases by about 3.2%, resulting in a broad kernel-wide slowdown. Measurements by Mel -Gorman [1] have shown a slowdown of 5-10% for some workloads. +Gorman [1]_ have shown a slowdown of 5-10% for some workloads. In contrast, the ORC unwinder has no effect on text size or runtime performance, because the debuginfo is out of band. So if you disable @@ -55,7 +58,7 @@ depending on the kernel config. ORC vs DWARF ------------- +============ ORC debuginfo's advantage over DWARF itself is that it's much simpler. It gets rid of the complex DWARF CFI state machine and also gets rid of @@ -65,7 +68,7 @@ mission critical oops code. The simpler debuginfo format also enables the unwinder to be much faster than DWARF, which is important for perf and lockdep. In a basic -performance test by Jiri Slaby [2], the ORC unwinder was about 20x +performance test by Jiri Slaby [2]_, the ORC unwinder was about 20x faster than an out-of-tree DWARF unwinder. (Note: That measurement was taken before some performance tweaks were added, which doubled performance, so the speedup over DWARF may be closer to 40x.) @@ -85,7 +88,7 @@ still be able to control the format, e.g. no complex state machines. ORC unwind table generation ---------------------------- +=========================== The ORC data is generated by objtool. With the existing compile-time stack metadata validation feature, objtool already follows all code @@ -133,7 +136,7 @@ objtool follows GCC code quite well. Unwinder implementation details -------------------------------- +=============================== Objtool generates the ORC data by integrating with the compile-time stack metadata validation feature, which is described in detail in @@ -154,7 +157,7 @@ subset of the table needs to be searched. Etymology ---------- +========= Orcs, fearsome creatures of medieval folklore, are the Dwarves' natural enemies. Similarly, the ORC unwinder was created in opposition to the @@ -162,7 +165,7 @@ complexity and slowness of DWARF. "Although Orcs rarely consider multiple solutions to a problem, they do excel at getting things done because they are creatures of action, not -thought." [3] Similarly, unlike the esoteric DWARF unwinder, the +thought." [3]_ Similarly, unlike the esoteric DWARF unwinder, the veracious ORC unwinder wastes no time or siloconic effort decoding variable-length zero-extended unsigned-integer byte-coded state-machine-based debug information entries. @@ -174,6 +177,6 @@ brutal, unyielding efficiency. ORC stands for Oops Rewind Capability. -[1] https://lkml.kernel.org/r/20170602104048.jkkzssljsompjdwy@suse.de -[2] https://lkml.kernel.org/r/d2ca5435-6386-29b8-db87-7f227c2b713a@suse.cz -[3] http://dustin.wikidot.com/half-orcs-and-orcs +.. [1] https://lkml.kernel.org/r/20170602104048.jkkzssljsompjdwy@suse.de +.. [2] https://lkml.kernel.org/r/d2ca5435-6386-29b8-db87-7f227c2b713a@suse.cz +.. [3] http://dustin.wikidot.com/half-orcs-and-orcs |