aboutsummaryrefslogtreecommitdiffstats
path: root/Documentation/x86
diff options
context:
space:
mode:
authorChangbin Du <changbin.du@gmail.com>2019-05-08 15:21:32 (GMT)
committerJonathan Corbet <corbet@lwn.net>2019-05-08 20:34:11 (GMT)
commit9d12f58fe91e5e72ef08afe9e3e66d1c755fc085 (patch)
treeb6a978c0c86478e81fe351a2bb5dd67c4452c502 /Documentation/x86
parent1cd7af509dc223905dce622c07ec62e26044e3c0 (diff)
downloadkernel_replicant_linux-9d12f58fe91e5e72ef08afe9e3e66d1c755fc085.zip
kernel_replicant_linux-9d12f58fe91e5e72ef08afe9e3e66d1c755fc085.tar.gz
kernel_replicant_linux-9d12f58fe91e5e72ef08afe9e3e66d1c755fc085.tar.bz2
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.rst1
-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 6e3c887..4535570 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 cd4b29b..d811576 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