Commit eadcaa3d authored by Tony Jones's avatar Tony Jones Committed by Arnaldo Carvalho de Melo
Browse files

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: default avatarTony Jones <tonyj@suse.de>
Link: http://lore.kernel.org/lkml/20200325164053.10177-1-tonyj@suse.de


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 0d33b343

tools/perf/Documentation/perf-config.txt

+8 −6
Original line number Diff line number Diff line
@@ -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).

tools/perf/Documentation/perf-record.txt

+12 −6
Original line number Diff line number Diff line
@@ -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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