Messages in this thread | | | From | Frederic Weisbecker <> | Subject | [RFC] perf: Dwarf cfi based user callchains | Date | Wed, 13 Oct 2010 07:06:52 +0200 |
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Hi,
This brings dwarf cfi based callchain for userspace apps that don't have frame pointers.
To test it, you can try:
perf record -g dwarf,24000 -e cycles:u ./hackbench 2 perf report
It seems to work but there are of course many things to improve:
- do only userspace profiling with that mode for now (the :u flag as above). The reason is that if you profile also the kernel, the user callchains will often start from vdso if the user made a syscall, and vdso doesn't have cfi informations, so we get stuck there. I need to find a solution for that, like doing a single frame pointer deref on the first entry (vdso) and continue with dwarves, but I need to know if we came from a syscall for that. Not sure yet how I'll handle that.
- it only works with .eh_frame, I think there is an elf section that is made almost the same but with few differences. I don't remember the name at that time but that needs a look.
- it's slow. A first improvement to make it faster is to support binary search from .eh_frame_hdr. This will probably be one of the next things I'll focus in. And the whole needs perhaps more caching and so on.
- only support for x86-32. I need to split some arch specific code from generic and add at least x86-64 support.
- there are still some callchains that are not unwind. I need to investigate.
This can be found in:
git://git.kernel.org/pub/scm/linux/kernel/git/frederic/random-tracing.git perf/unwind-v1
Thanks, Frederic ---
Frederic Weisbecker (9): uaccess: Make copy_from_user_nmi() globally available perf: Add ability to dump user regs perf: Add ability to dump part of the user stack perf: Don't record frame pointer based user stacktraces if we dump stack and regs perf: Support for dwarf mode callchain on perf record perf: Build with dwarf cfi perf: Support for error passed over pointers perf: Add libunwind dependency for dwarf cfi unwinding perf: Support for dwarf cfi unwinding on post processing
arch/x86/include/asm/uaccess.h | 5 + arch/x86/kernel/cpu/perf_event.c | 4 +- include/asm-generic/uaccess.h | 4 + include/linux/perf_event.h | 15 +- kernel/perf_event.c | 182 +++++- tools/perf/Makefile | 23 +- tools/perf/builtin-record.c | 76 +++- tools/perf/builtin-report.c | 9 +- tools/perf/feature-tests.mak | 14 + tools/perf/perf.h | 5 + tools/perf/util/callchain.c | 35 +- tools/perf/util/callchain.h | 19 +- tools/perf/util/event.c | 29 + tools/perf/util/event.h | 7 + tools/perf/util/include/linux/err.h | 24 + tools/perf/util/unwind.c | 1077 +++++++++++++++++++++++++++++++++++ 16 files changed, 1485 insertions(+), 43 deletions(-)
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