[lkml]   [2020]   [Apr]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH 01/31] perf callchain: Update docs regarding kernel/user space unwinding
From: Tony Jones <>

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 <>
Signed-off-by: Arnaldo Carvalho de Melo <>
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..f16d8a71d3f5 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.

- 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/--call-graph options).

- 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_*).

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.

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

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
+ 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
 \ /
  Last update: 2020-04-03 16:55    [W:0.088 / U:2.616 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site