The following commit has been merged into the perf/urgent branch of tip: Commit-ID: eadcaa3dfd706bbf46682c8b8b5979262443c3c3 Gitweb: https://git.kernel.org/tip/eadcaa3dfd706bbf46682c8b8b5979262443c3c3 Author: Tony Jones <tonyj@xxxxxxx> AuthorDate: Wed, 25 Mar 2020 09:40:53 -07:00 Committer: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> CommitterDate: Wed, 25 Mar 2020 16:13:21 -03:00 perf callchain: Update docs regarding kernel/user space unwinding 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@xxxxxxx> Link: http://lore.kernel.org/lkml/20200325164053.10177-1-tonyj@xxxxxxx Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> --- 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 8ead555..f16d8a7 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/--call-graph 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 7f4db75..b25e028 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
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