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Subject[PATCH] perf tools: update docs regarding kernel/user space unwinding
Date
The method of unwinding for kernel space is defined by the kernel config, 
not by the value of --call-graph. Improve the documentation to reflect
this.

Signed-off-by: Tony Jones <tonyj@suse.de>

---
tools/perf/Documentation/perf-config.txt | 14 ++++++++------
tools/perf/Documentation/perf-record.txt | 18 ++++++++++++------
2 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/tools/perf/Documentation/perf-config.txt b/tools/perf/Documentation/perf-config.txt
index 8ead55593984..88cf35fbedc5 100644
--- a/tools/perf/Documentation/perf-config.txt
+++ b/tools/perf/Documentation/perf-config.txt
@@ -405,14 +405,16 @@ ui.*::
This option is only applied to TUI.

call-graph.*::
- When sub-commands 'top' and 'report' work with -g/—-children
- there're options in control of call-graph.
+ The following controls the handling of call-graphs (obtained via the
+ -g/--callgraph options).

call-graph.record-mode::
- The record-mode can be 'fp' (frame pointer), 'dwarf' and 'lbr'.
- The value of 'dwarf' is effective only if perf detect needed library
- (libunwind or a recent version of libdw).
- 'lbr' only work for cpus that support it.
+ The mode for user space can be 'fp' (frame pointer), 'dwarf'
+ and 'lbr'. The value 'dwarf' is effective only if libunwind
+ (or a recent version of libdw) is present on the system;
+ the value 'lbr' only works for certain cpus. The method for
+ kernel space is controlled not by this option but by the
+ kernel config (CONFIG_UNWINDER_*).

call-graph.dump-size::
The size of stack to dump in order to do post-unwinding. Default is 8192 (byte).
diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 7f4db7592467..b25e028458e2 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -237,16 +237,22 @@ OPTIONS
option and remains only for backward compatibility. See --event.

-g::
- Enables call-graph (stack chain/backtrace) recording.
+ Enables call-graph (stack chain/backtrace) recording for both
+ kernel space and user space.

--call-graph::
Setup and enable call-graph (stack chain/backtrace) recording,
- implies -g. Default is "fp".
+ implies -g. Default is "fp" (for user space).

- Allows specifying "fp" (frame pointer) or "dwarf"
- (DWARF's CFI - Call Frame Information) or "lbr"
- (Hardware Last Branch Record facility) as the method to collect
- the information used to show the call graphs.
+ The unwinding method used for kernel space is dependent on the
+ unwinder used by the active kernel configuration, i.e
+ CONFIG_UNWINDER_FRAME_POINTER (fp) or CONFIG_UNWINDER_ORC (orc)
+
+ Any option specified here controls the method used for user space.
+
+ Valid options are "fp" (frame pointer), "dwarf" (DWARF's CFI -
+ Call Frame Information) or "lbr" (Hardware Last Branch Record
+ facility).

In some systems, where binaries are build with gcc
--fomit-frame-pointer, using the "fp" method will produce bogus
--
2.25.0
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