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perf callchain: Update docs regarding kernel/user space unwinding

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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>
Link: http://lore.kernel.org/lkml/20200325164053.10177-1-tonyj@suse.de
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Tony Jones 2020-03-25 09:40:53 -07:00 committed by Arnaldo Carvalho de Melo
parent 0d33b34352
commit eadcaa3dfd
2 changed files with 20 additions and 12 deletions
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14
tools/perf/Documentation/perf-config.txt
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@ -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).

18
tools/perf/Documentation/perf-record.txt
View file

@ -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