From aad2b21c151273fa7abc419dac51a980eff1dd17 Mon Sep 17 00:00:00 2001 From: Kan Liang Date: Mon, 5 Jan 2015 13:23:04 -0500 Subject: perf tools: Enable LBR call stack support Currently, there are two call chain recording options, fp and dwarf. Haswell has a new feature that utilizes the existing LBR facility to record call chains. Kernel side LBR support code provides this as a third option to record call chains. This patch enables the lbr call stack support on the tooling side. LBR call stack has some limitations: - It reuses current LBR facility, so LBR call stack and branch record can not be enabled at the same time. - It is only available for user-space callchains. However, it also offers some advantages: - LBR call stack can work on user apps which don't have frame-pointers or dwarf debug info compiled. It is a good alternative when nothing else works. Tested-by: Jiri Olsa Signed-off-by: Kan Liang Signed-off-by: Peter Zijlstra (Intel) Cc: Adrian Hunter Cc: Anshuman Khandual Cc: Arnaldo Carvalho de Melo Cc: Cody P Schafer Cc: David Ahern Cc: Don Zickus Cc: Jacob Shin Cc: Jiri Olsa Cc: Linus Torvalds Cc: Masanari Iida Cc: Namhyung Kim Cc: Paul Mackerras Cc: Rodrigo Campos Cc: Stephane Eranian Cc: Sukadev Bhattiprolu Link: http://lkml.kernel.org/r/1420482185-29830-2-git-send-email-kan.liang@intel.com Signed-off-by: Ingo Molnar --- tools/perf/Documentation/perf-record.txt | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'tools/perf/Documentation') diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt index 31e977459c51..1c7e50f62b1f 100644 --- a/tools/perf/Documentation/perf-record.txt +++ b/tools/perf/Documentation/perf-record.txt @@ -115,13 +115,19 @@ OPTIONS implies -g. Allows specifying "fp" (frame pointer) or "dwarf" - (DWARF's CFI - Call Frame Information) as the method to collect + (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. In some systems, where binaries are build with gcc --fomit-frame-pointer, using the "fp" method will produce bogus call graphs, using "dwarf", if available (perf tools linked to the libunwind library) should be used instead. + Using the "lbr" method doesn't require any compiler options. It + will produce call graphs from the hardware LBR registers. The + main limition is that it is only available on new Intel + platforms, such as Haswell. It can only get user call chain. It + doesn't work with branch stack sampling at the same time. -q:: --quiet:: -- cgit v1.2.3