From: Kan Liang <kan.li...@intel.com> This is the user space patch for Haswell LBR call stack support. For many profiling tasks we need the callgraph. For example we often need to see the caller of a lock or the caller of a memcpy or other library function to actually tune the program. Frame pointer unwinding is efficient and works well. But frame pointers are off by default on 64bit code (and on modern 32bit gccs), so there are many binaries around that do not use frame pointers. Profiling unchanged production code is very useful in practice. On some CPUs frame pointer also has a high cost. Dwarf2 unwinding also does not always work and is extremely slow (upto 20% overhead).
Haswell has a new feature that utilizes the existing Last Branch Record facility to record call chains. When the feature is enabled, function call will be collected as normal, but as return instructions are executed the last captured branch record is popped from the on-chip LBR registers. The LBR call stack facility provides an alternative to get callgraph. It has some limitations too, but should work in most cases and is significantly faster than dwarf. Frame pointer unwinding is still the best default, but LBR call stack is a good alternative when nothing else works. Please find the kernel part patch at https://lkml.org/lkml/2014/11/6/432 Changes since v1 - Update help document - Force exclude_user to 0 with warning in LBR call stack - Dump both lbr and fp info when report -D - Reconstruct thread__resolve_callchain_sample and split it into two patches - Use has_branch_callstack function to check LBR call stack available Changes since v2 - Rebase to 025ce5d33373 Changes since v3 - Rebase to cc502c23aadf - Separated function for lbr call stack sample resolve and print - Some minor changes according to comments Changes since V4 - Rebase to 09a6a1b - Falling back to framepointers if LBR not availabe, and warning user Changes since V5 - Only remove the 2/3 and part of 1/3 which have already been merged. Kan Liang (2): perf tools: enable LBR call stack support perf tools: Construct LBR call chain tools/perf/Documentation/perf-record.txt | 8 ++- tools/perf/builtin-record.c | 6 +- tools/perf/builtin-report.c | 2 + tools/perf/util/callchain.c | 8 +++ tools/perf/util/callchain.h | 1 + tools/perf/util/evsel.c | 21 ++++++- tools/perf/util/evsel.h | 4 ++ tools/perf/util/machine.c | 102 +++++++++++++++++++++++++++---- tools/perf/util/session.c | 64 +++++++++++++++++-- 9 files changed, 193 insertions(+), 23 deletions(-) -- 1.8.3.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
